Subject: Re: [PATCH v3 4/4] powerpc/mpc5200: Add mpc5200-spi (non-PSC) device driver

From: David Brownell <[email-masked]>
Date: Sun, 27 Jul 2008 14:41:20 -0700

On Friday 25 July 2008, Grant Likely wrote:
> From: Grant Likely <[email-masked]>
> 
> Adds support for the dedicated SPI device on the Freescale MPC5200(b)
> SoC.

It'd be a bit more clear if you said dedicated SPI "controller";
"device" sounds like it's a "struct spi_device".

Capsule summary:  fault handling needs work.  (Details below.)

> Signed-off-by: Grant Likely <[email-masked]>
> ---
> 
>  drivers/spi/Kconfig             |    8 +
>  drivers/spi/Makefile            |    1 
>  drivers/spi/mpc52xx_spi.c       |  595 +++++++++++++++++++++++++++++++++++++++
>  include/linux/spi/mpc52xx_spi.h |   10 +
>  4 files changed, 614 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
> index 2303521..68e4a4a 100644
> --- a/drivers/spi/Kconfig
> +++ b/drivers/spi/Kconfig
> @@ -116,6 +116,14 @@ config SPI_LM70_LLP
>  	  which interfaces to an LM70 temperature sensor using
>  	  a parallel port.
>  
> +config SPI_MPC52xx
> +	tristate "Freescale MPC52xx SPI (non-PSC) controller support"
> +	depends on PPC_MPC52xx && SPI
> +	select SPI_MASTER_OF
> +	help
> +	  This drivers supports the MPC52xx SPI controller in master SPI
> +	  mode.
> +
>  config SPI_MPC52xx_PSC
>  	tristate "Freescale MPC52xx PSC SPI controller"
>  	depends on PPC_MPC52xx && EXPERIMENTAL
> diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
> index 7fca043..340b878 100644
> --- a/drivers/spi/Makefile
> +++ b/drivers/spi/Makefile
> @@ -22,6 +22,7 @@ obj-$(CONFIG_SPI_PXA2XX)		+= pxa2xx_spi.o
>  obj-$(CONFIG_SPI_OMAP_UWIRE)		+= omap_uwire.o
>  obj-$(CONFIG_SPI_OMAP24XX)		+= omap2_mcspi.o
>  obj-$(CONFIG_SPI_MPC52xx_PSC)		+= mpc52xx_psc_spi.o
> +obj-$(CONFIG_SPI_MPC52xx)		+= mpc52xx_spi.o
>  obj-$(CONFIG_SPI_MPC83xx)		+= spi_mpc83xx.o
>  obj-$(CONFIG_SPI_S3C24XX_GPIO)		+= spi_s3c24xx_gpio.o
>  obj-$(CONFIG_SPI_S3C24XX)		+= spi_s3c24xx.o
> diff --git a/drivers/spi/mpc52xx_spi.c b/drivers/spi/mpc52xx_spi.c
> new file mode 100644
> index 0000000..453690f
> --- /dev/null
> +++ b/drivers/spi/mpc52xx_spi.c
> @@ -0,0 +1,595 @@
> +/*
> + * MPC52xx SPI master driver.
> + * Copyright (C) 2008 Secret Lab Technologies Ltd.
> + *
> + * This is the driver for the MPC5200's dedicated SPI device (not for a
> + * PSC in SPI mode)
> + */
> +
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/errno.h>
> +#include <linux/of_platform.h>
> +#include <linux/interrupt.h>
> +#include <linux/delay.h>
> +#include <linux/spi/spi.h>
> +#include <linux/spi/mpc52xx_spi.h>
> +#include <linux/of_spi.h>
> +#include <linux/io.h>
> +#include <asm/time.h>
> +#include <asm/mpc52xx.h>
> +
> +MODULE_AUTHOR("Grant Likely <[email-masked]>");
> +MODULE_DESCRIPTION("MPC52xx SPI (non-PSC) Driver");
> +MODULE_LICENSE("GPL");
> +
> +/* Register offsets */
> +#define SPI_CTRL1	0x00
> +#define SPI_CTRL1_SPIE		(1 << 7)
> +#define SPI_CTRL1_SPE		(1 << 6)
> +#define SPI_CTRL1_MSTR		(1 << 4)
> +#define SPI_CTRL1_CPOL		(1 << 3)
> +#define SPI_CTRL1_CPHA		(1 << 2)
> +#define SPI_CTRL1_SSOE		(1 << 1)
> +#define SPI_CTRL1_LSBFE		(1 << 0)
> +
> +#define SPI_CTRL2	0x01
> +#define SPI_BRR		0x04
> +
> +#define SPI_STATUS	0x05
> +#define SPI_STATUS_SPIF		(1 << 7)
> +#define SPI_STATUS_WCOL		(1 << 6)
> +#define SPI_STATUS_MODF		(1 << 4)
> +
> +#define SPI_DATA	0x09
> +#define SPI_PORTDATA	0x0d
> +#define SPI_DATADIR	0x10
> +
> +/* FSM state return values */
> +#define FSM_STOP	0
> +#define FSM_POLL	1
> +#define FSM_CONTINUE	2
> +
> +/* Driver internal data */
> +struct mpc52xx_spi {
> +	struct spi_master *master;
> +	u32 sysclk;
> +	void __iomem *regs;
> +	int irq0;	/* MODF irq */
> +	int irq1;	/* SPIF irq */
> +	int ipb_freq;
> +
> +	/* Statistics */
> +	int msg_count;
> +	int wcol_count;
> +	int wcol_ticks;
> +	u32 wcol_tx_timestamp;
> +	int modf_count;
> +	int byte_count;
> +
> +	/* Hooks for platform modification of behaviour */
> +	void (*premessage)(struct spi_message *m, void *context);
> +	void *premessage_context;
> +
> +	struct list_head queue;		/* queue of pending messages */
> +	spinlock_t lock;
> +	struct work_struct work;
> +
> +
> +	/* Details of current transfer (length, and buffer pointers) */
> +	struct spi_message *message;	/* current message */
> +	struct spi_transfer *transfer;	/* current transfer */
> +	int (*state)(int irq, struct mpc52xx_spi *ms, u8 status, u8 data);
> +	int len;
> +	int timestamp;
> +	u8 *rx_buf;
> +	const u8 *tx_buf;
> +	int cs_change;
> +};
> +
> +/*
> + * CS control function
> + */
> +static void mpc52xx_spi_chipsel(struct mpc52xx_spi *ms, int value)
> +{
> +	if (value)
> +		writeb(0, ms->regs + SPI_PORTDATA); /* Assert SS pin */
> +	else
> +		writeb(0x08, ms->regs + SPI_PORTDATA); /* Deassert SS pin */
> +}
> +
> +/*
> + * Start a new transfer.  This is called both by the idle state
> + * for the first transfer in a message, and by the wait state when the
> + * previous transfer in a message is complete.
> + */
> +static void mpc52xx_spi_start_transfer(struct mpc52xx_spi *ms)
> +{
> +	ms->rx_buf = ms->transfer->rx_buf;
> +	ms->tx_buf = ms->transfer->tx_buf;
> +	ms->len = ms->transfer->len;
> +
> +	/* Activate the chip select */
> +	if (ms->cs_change)
> +		mpc52xx_spi_chipsel(ms, 1);
> +	ms->cs_change = ms->transfer->cs_change;
> +
> +	/* Write out the first byte */
> +	ms->wcol_tx_timestamp = get_tbl();
> +	if (ms->tx_buf)
> +		writeb(*ms->tx_buf++, ms->regs + SPI_DATA);
> +	else
> +		writeb(0, ms->regs + SPI_DATA);
> +}
> +
> +/* Forward declaration of state handlers */
> +static int mpc52xx_spi_fsmstate_transfer(int irq, struct mpc52xx_spi *ms,
> +					 u8 status, u8 data);
> +static int mpc52xx_spi_fsmstate_wait(int irq, struct mpc52xx_spi *ms,
> +				     u8 status, u8 data);
> +
> +/*
> + * IDLE state
> + *
> + * No transfers are in progress; if another transfer is pending then retrieve
> + * it and kick it off.  Otherwise, stop processing the state machine
> + */
> +static int
> +mpc52xx_spi_fsmstate_idle(int irq, struct mpc52xx_spi *ms, u8 status, u8 data)
> +{
> +	struct spi_message *m;
> +	struct spi_device *spi;
> +	int spr, sppr;
> +	u8 ctrl1;
> +
> +	if (status && (irq != NO_IRQ))
> +		dev_err(&ms->master->dev, "spurious irq, status=0x%.2x\n",
> +			status);
> +
> +	/* Check if there is another transfer waiting */
> +	if (list_empty(&ms->queue))
> +		return FSM_STOP;

As Daniel noted:  the queue is protected by the spinlock,
so grab that first.  And you said you'd fix that.

> +
> +	/* Get the next message */
> +	spin_lock(&ms->lock);
> +
> +	/* Call the pre-message hook with a pointer to the next
> +	 * message.  The pre-message hook may enqueue a new message for
> +	 * changing the chip select value to the head of the queue */
> +	m = list_first_entry(&ms->queue, struct spi_message, queue);

I don't quite see the point of this pre-message extension;
the kerneldoc there is kind of opaque.  How could it queue a
new message that would affect the head of the queue??  The
relevant data structures aren't even visible to that function!

That said:

> +	if (ms->premessage)
> +		ms->premessage(m, ms->premessage_context);
> +
> +	/* reget the head of the queue (the premessage hook may have enqueued
> +	 * something before it.) and drop the spinlock */
> +	ms->message = list_first_entry(&ms->queue, struct spi_message, queue);

	if (ms->premessage) {
		hook();
		ms->message = ...
	} else
		ms->message = m;

... would be more clear to me, at least if I could see a way
for that "premessage hook" to modify the queue in any way other
than calling spi_transfer() to *append* an entry.

Also, it'd be more clear to have this function use "m" for its
working state not "ms->message" ... and at least some versions
of GCC would generate much better code that way, since they
wouldn't need to reload the register.

> +	list_del_init(&ms->message->queue);
> +	spin_unlock(&ms->lock);
> +
> +	/* Setup the controller parameters */
> +	ctrl1 = SPI_CTRL1_SPIE | SPI_CTRL1_SPE | SPI_CTRL1_MSTR;
> +	spi = ms->message->spi;
> +	if (spi->mode & SPI_CPHA)
> +		ctrl1 |= SPI_CTRL1_CPHA;
> +	if (spi->mode & SPI_CPOL)
> +		ctrl1 |= SPI_CTRL1_CPOL;
> +	if (spi->mode & SPI_LSB_FIRST)
> +		ctrl1 |= SPI_CTRL1_LSBFE;
> +	writeb(ctrl1, ms->regs + SPI_CTRL1);
> +
> +	/* Setup the controller speed */
> +	/* minimum divider is '2'.  Also, add '1' to force rounding up. */
> +	sppr = ((ms->ipb_freq / ms->message->spi->max_speed_hz) + 1) >> 1;
> +	spr = 0;
> +	if (sppr < 1)
> +		sppr = 1;
> +	while (((sppr - 1) & ~0x7) != 0) {
> +		sppr = (sppr + 1) >> 1; /* add '1' to force rounding up */
> +		spr++;
> +	}
> +	sppr--;		/* sppr quantity in register is offset by 1 */
> +	if (spr > 7) {
> +		/* Don't overrun limits of SPI baudrate register */
> +		spr = 7;
> +		sppr = 7;

So here you're setting the SPI clock rate faster than the spi_device
says it can handle?  Bad idea!  There should be an error report.  In
this case, it's best done in the setup() callback -- it could just
compute and save the SPI_BRR value in chip-specific data -- so that
you never get errors at this point.

> +	}
> +	writeb(sppr << 4 | spr, ms->regs + SPI_BRR); /* Set speed */

It'd be better to have that "set speed" logic be a subroutine, so
that you can use it for both per-message setup and for per-transfer
overrides.

In a similar vein, you're ignoring spi->bits_per_word completely...
looks like you're assuming it's always eight.

> +
> +	ms->cs_change = 1;
> +	ms->transfer = container_of(ms->message->transfers.next,
> +				    struct spi_transfer, transfer_list);
> +
> +	mpc52xx_spi_start_transfer(ms);
> +	ms->state = mpc52xx_spi_fsmstate_transfer;
> +
> +#if defined(VERBOSE_DEBUG)
> +	dev_info(&ms->master->dev, "msg:%p, max_speed:%i, brr:%.2x\n",

So just make this dev_vdbg() ... not #ifdef + dev_info().

> +		 ms->message, ms->message->spi->max_speed_hz,
> +		 readb(ms->regs + SPI_BRR));
> +#endif
> +
> +	return FSM_CONTINUE;
> +}
> +
> +/*
> + * TRANSFER state
> + *
> + * In the middle of a transfer.  If the SPI core has completed processing
> + * a byte, then read out the received data and write out the next byte
> + * (unless this transfer is finished; in which case go on to the wait
> + * state)
> + */
> +static int mpc52xx_spi_fsmstate_transfer(int irq, struct mpc52xx_spi *ms,
> +					 u8 status, u8 data)
> +{
> +	if (!status)
> +		return ms->irq0 == NO_IRQ ? FSM_POLL : FSM_STOP;
> +
> +	if (status & SPI_STATUS_WCOL) {
> +		/* The SPI device is stoopid.  At slower speeds, it may raise
> +		 * the SPIF flag before the state machine is actually finished.
> +		 * which causes a collision (internal to the state machine
> +		 * only).  The manual recommends inserting a delay between
> +		 * receving the interrupt and sending the next byte, but
> +		 * it can also be worked around simply by retrying the
> +		 * transfer which is what we do here. */
> +		ms->wcol_count++;
> +		ms->wcol_ticks += get_tbl() - ms->wcol_tx_timestamp;
> +		ms->wcol_tx_timestamp = get_tbl();
> +		data = 0;
> +		if (ms->tx_buf)
> +			data = *(ms->tx_buf-1);
> +		writeb(data, ms->regs + SPI_DATA); /* try again */
> +		return FSM_CONTINUE;
> +	} else if (status & SPI_STATUS_MODF) {
> +		ms->modf_count++;
> +		dev_err(&ms->master->dev, "mod fault\n");

Is this "mode fault"?  A "mod fault" would be one of the
weak episodes of "The Mod Squad". ;)

> +		mpc52xx_spi_chipsel(ms, 0);
> +		ms->message->status = -EIO;
> +		if (ms->message->complete)
> +			ms->message->complete(ms->message->context);

All messages must have completion functions; don't check.

And drop the spinlock before calling the completion, since
it's normal for such functions to resubmit ... and hence
re-enter this driver.

> +		ms->state = mpc52xx_spi_fsmstate_idle;
> +		return FSM_CONTINUE;
> +	}
> +
> +	/* Read data out of the spi device */
> +	ms->byte_count++;
> +	if (ms->rx_buf)
> +		*ms->rx_buf++ = data;
> +
> +	/* Is the transfer complete? */
> +	ms->len--;
> +	if (ms->len == 0) {
> +		ms->timestamp = get_tbl();
> +		ms->timestamp += ms->transfer->delay_usecs * tb_ticks_per_usec;
> +		ms->state = mpc52xx_spi_fsmstate_wait;
> +		return FSM_CONTINUE;
> +	}
> +
> +	/* Write out the next byte */
> +	ms->wcol_tx_timestamp = get_tbl();
> +	if (ms->tx_buf)
> +		writeb(*ms->tx_buf++, ms->regs + SPI_DATA);
> +	else
> +		writeb(0, ms->regs + SPI_DATA);
> +
> +	return FSM_CONTINUE;
> +}
> +
> +/*
> + * WAIT state
> + *
> + * A transfer has completed; need to wait for the delay period to complete
> + * before starting the next transfer
> + */
> +static int
> +mpc52xx_spi_fsmstate_wait(int irq, struct mpc52xx_spi *ms, u8 status, u8 data)
> +{
> +	if (status && irq != NO_IRQ)
> +		dev_err(&ms->master->dev, "spurious irq, status=0x%.2x\n",
> +			status);
> +
> +	if (((int)get_tbl()) - ms->timestamp < 0)
> +		return FSM_POLL;
> +
> +	ms->message->actual_length += ms->transfer->len;

Subtract ms->len though, yes?  And abort the transfer if ms->len is
nonzero (controller reported an error or whatever).

> +
> +	/* Check if there is another transfer in this message.  If there
> +	 * aren't then deactivate CS, notify sender, and drop back to idle
> +	 * to start the next message. */
> +	if (ms->transfer->transfer_list.next == &ms->message->transfers) {
> +		ms->msg_count++;
> +		mpc52xx_spi_chipsel(ms, 0);
> +		ms->message->status = 0;
> +		if (ms->message->complete)
> +			ms->message->complete(ms->message->context);

See above about calling completions.

> +		ms->state = mpc52xx_spi_fsmstate_idle;
> +		return FSM_CONTINUE;
> +	}
> +
> +	/* There is another transfer; kick it off */
> +
> +	if (ms->cs_change)
> +		mpc52xx_spi_chipsel(ms, 0);
> +
> +	ms->transfer = container_of(ms->transfer->transfer_list.next,
> +				    struct spi_transfer, transfer_list);
> +	mpc52xx_spi_start_transfer(ms);
> +	ms->state = mpc52xx_spi_fsmstate_transfer;
> +	return FSM_CONTINUE;
> +}
> +
> +/*
> + * IRQ handler
> + */
> +static irqreturn_t mpc52xx_spi_irq(int irq, void *_ms)
> +{
> +	struct mpc52xx_spi *ms = _ms;
> +	int rc = FSM_CONTINUE;
> +	u8 status, data;
> +
> +	while (rc == FSM_CONTINUE) {
> +		/* Interrupt cleared by read of STATUS followed by
> +		 * read of DATA registers*/
> +		status = readb(ms->regs + SPI_STATUS);
> +		data = readb(ms->regs + SPI_DATA); /* clear status */
> +		rc = ms->state(irq, ms, status, data);
> +	}
> +
> +	if (rc == FSM_POLL)
> +		schedule_work(&ms->work);

When the POLL return is from mpc52xx_spi_fsmstate_wait() should
this maybe be a schedule_work_delayed() ... ?

> +
> +	return IRQ_HANDLED;
> +}
> +
> +/*
> + * Workqueue method of running the state machine
> + */
> +static void mpc52xx_spi_wq(struct work_struct *work)
> +{
> +	struct mpc52xx_spi *ms = container_of(work, struct mpc52xx_spi, work);
> +	mpc52xx_spi_irq(NO_IRQ, ms);
> +}
> +
> +/*
> + * spi_master callbacks
> + */
> +
> +static int mpc52xx_spi_setup(struct spi_device *spi)
> +{
> +	return 0;

Very unhealthy.  This is claiming success for *ALL* settings,
even invalid ones.  You should validate things here:

  - spi->max_speed_hz is within range of what this supports.

  - (spi->mode & ~(SPI_CPOL|SPI_CPHA|SPI_LSB_FIRST)) == 0
	... since those are the only mode bits you support

  - spi->bits_per_word is valid ... I think that means 8
    (or, synonymously, 0), but I can't tell.

  - spi->chip_select is valid

> +}
> +
> +static int mpc52xx_spi_transfer(struct spi_device *spi, struct spi_message *m)
> +{
> +	struct mpc52xx_spi *ms = spi_master_get_devdata(spi->master);
> +	unsigned long flags;
> +
> +	m->actual_length = 0;
> +	m->status = -EINPROGRESS;

Before adding this to the queue, I suggest you verify that you
can handle this.  Your state machine assumes you did that, but
you aren't ...

Without changing the body of the code you've written already,
I suggest just scanning all the transfers in this message for
bits_per_word or max_speed_hz being nonzero, returning -EINVAL
if any transfer said to not use defaults for that spi_device.
And maybe verify that m->complete is non-null.

> +
> +	spin_lock_irqsave(&ms->lock, flags);
> +	list_add_tail(&m->queue, &ms->queue);
> +	spin_unlock_irqrestore(&ms->lock, flags);

> +	schedule_work(&ms->work);

That looks goofy.  The workqueue just fakes out an IRQ;
but you don't check whether your state machine is active
before doing that, so a *real* IRQ could come in at the
same time and cause confusion.

Probably better to

	if (ms->state == mpc52xx_spi_fsmstate_idle)
		schedule_work()
	spin_unlock_irqrestore(...)

maybe even just call mpc52xx_spi_fsmstate_idle() directly
instead of punting to a (possibly busy) workqueue.

> +
> +	return 0;
> +}
> +
> +/*
> + * Hook to modify premessage hook

Opaque; why does this exist?  If it's not well motivated I'd
rather not see it.  And if it's well motivated I wonder why
it should be specific to this driver ...

> + */
> +void mpc52xx_spi_set_premessage_hook(struct spi_master *master,
> +				     void (*hook)(struct spi_message *m,
> +						  void *context),
> +				     void *hook_context)
> +{
> +	struct mpc52xx_spi *ms = spi_master_get_devdata(master);
> +	ms->premessage = hook;
> +	ms->premessage_context = hook_context;

These ms->premessage values may be changed while something is
accessing them ... you should hold ms->lock to prevent that.

> +}
> +EXPORT_SYMBOL(mpc52xx_spi_set_premessage_hook);

EXPORT_SYMBOL_GPL?

> +
> +/*
> + * SysFS files
> + */
> +static int
> +*mpc52xx_spi_sysfs_get_counter(struct mpc52xx_spi *ms, const char *name)
> +{
> +	if (strcmp(name, "msg_count") == 0)
> +		return &ms->msg_count;
> +	if (strcmp(name, "byte_count") == 0)
> +		return &ms->byte_count;
> +	if (strcmp(name, "wcol_count") == 0)
> +		return &ms->wcol_count;
> +	if (strcmp(name, "wcol_ticks") == 0)
> +		return &ms->wcol_ticks;
> +	if (strcmp(name, "modf_count") == 0)
> +		return &ms->modf_count;
> +	return NULL;
> +}
> +
> +static ssize_t mpc52xx_spi_show_count(struct device *dev,
> +				      struct device_attribute *attr,
> +				      char *buf)
> +{
> +	struct spi_master *master = container_of(dev, struct spi_master, dev);
> +	struct mpc52xx_spi *ms = spi_master_get_devdata(master);
> +	int *counter;
> +
> +	counter = mpc52xx_spi_sysfs_get_counter(ms, attr->attr.name);
> +	if (!counter)
> +		return sprintf(buf, "error\n");
> +	return sprintf(buf, "%d\n", *counter);
> +}
> +
> +static ssize_t mpc52xx_spi_set_count(struct device *dev,
> +				     struct device_attribute *attr,
> +				     const char *buf, size_t count)
> +{
> +	struct spi_master *master = container_of(dev, struct spi_master, dev);
> +	struct mpc52xx_spi *ms = spi_master_get_devdata(master);
> +	int *counter;
> +	int value = simple_strtoul(buf, NULL, 0);

Checkpatch suggests strict_strtoul(), which would indeed be better...

> +
> +	counter = mpc52xx_spi_sysfs_get_counter(ms, attr->attr.name);
> +	if (counter)
> +		*counter = value;
> +	return count;
> +}
> +
> +DEVICE_ATTR(msg_count, 0644, mpc52xx_spi_show_count, mpc52xx_spi_set_count);
> +DEVICE_ATTR(byte_count, 0644, mpc52xx_spi_show_count, mpc52xx_spi_set_count);
> +DEVICE_ATTR(wcol_count, 0644, mpc52xx_spi_show_count, mpc52xx_spi_set_count);
> +DEVICE_ATTR(wcol_ticks, 0644, mpc52xx_spi_show_count, mpc52xx_spi_set_count);
> +DEVICE_ATTR(modf_count, 0644, mpc52xx_spi_show_count, mpc52xx_spi_set_count);
> +
> +/*
> + * OF Platform Bus Binding
> + */
> +static int __devinit mpc52xx_spi_of_probe(struct of_device *op,
> +					  const struct of_device_id *match)
> +{
> +	struct spi_master *master;
> +	struct mpc52xx_spi *ms;
> +	void __iomem *regs;
> +	const u32 *prop;
> +	int rc, len;
> +
> +	/* MMIO registers */
> +	dev_dbg(&op->dev, "probing mpc5200 SPI device\n");
> +	regs = of_iomap(op->node, 0);
> +	if (!regs)
> +		return -ENODEV;
> +
> +	/* initialize the device */
> +	writeb(SPI_CTRL1_SPIE | SPI_CTRL1_SPE | SPI_CTRL1_MSTR, regs+SPI_CTRL1);
> +	writeb(0x0, regs + SPI_CTRL2);
> +	writeb(0xe, regs + SPI_DATADIR);	/* Set output pins */
> +	writeb(0x8, regs + SPI_PORTDATA);	/* Deassert /SS signal */
> +
> +	/* Clear the status register and re-read it to check for a MODF
> +	 * failure.  This driver cannot currently handle multiple masters
> +	 * on the SPI bus.  This fault will also occur if the SPI signals
> +	 * are not connected to any pins (port_config setting) */
> +	readb(regs + SPI_STATUS);
> +	readb(regs + SPI_DATA);
> +	if (readb(regs + SPI_STATUS) & SPI_STATUS_MODF) {
> +		dev_err(&op->dev, "mode fault; is port_config correct?\n");
> +		return -EIO;
> +	}
> +
> +	dev_dbg(&op->dev, "allocating spi_master struct\n");
> +	master = spi_alloc_master(&op->dev, sizeof *ms);
> +	if (!master)
> +		return -ENOMEM;
> +	master->bus_num = -1;
> +	master->num_chipselect = 1;
> +	prop = of_get_property(op->node, "num-slaves", &len);
> +	if (prop && len >= sizeof(*prop))
> +		master->num_chipselect = *prop;

But you don't actually handle more than one chipselect, do you?
Either add full support for them, or rip this out and make sure
that mpc52xx_spi_setup only allows chipselect zero.

> +
> +	master->setup = mpc52xx_spi_setup;
> +	master->transfer = mpc52xx_spi_transfer;
> +	dev_set_drvdata(&op->dev, master);
> +
> +	ms = spi_master_get_devdata(master);
> +	ms->master = master;
> +	ms->regs = regs;
> +	ms->irq0 = irq_of_parse_and_map(op->node, 0);
> +	ms->irq1 = irq_of_parse_and_map(op->node, 1);
> +	ms->state = mpc52xx_spi_fsmstate_idle;
> +	ms->ipb_freq = mpc52xx_find_ipb_freq(op->node);
> +	spin_lock_init(&ms->lock);
> +	INIT_LIST_HEAD(&ms->queue);
> +	INIT_WORK(&ms->work, mpc52xx_spi_wq);
> +
> +	dev_dbg(&op->dev, "registering spi_master struct\n");
> +	rc = spi_register_master(master);
> +	if (rc < 0)
> +		goto err_register;
> +
> +	/* Decide if interrupts can be used */
> +	if ((ms->irq0 != NO_IRQ) && (ms->irq1 != NO_IRQ)) {

I understand that NO_IRQ is supposed to vanish everywhere,
so these tests should become "if (ms->irq0 && ms->irq1)".

That said ... with two distinct interrupts, I'm thinking
there must be a better solution than having them do exactly
the same thing.

Plus, a more informative labeling policy would be passing
dev_name(&spi_master->dev) ...

> +		rc = request_irq(ms->irq0, mpc52xx_spi_irq, IRQF_SAMPLE_RANDOM,
> +				  "mpc5200-spi-modf", ms);
> +		rc |= request_irq(ms->irq1, mpc52xx_spi_irq, IRQF_SAMPLE_RANDOM,
> +				  "mpc5200-spi-spiF", ms);

I'm not a fan of that "rc |=" idiom, but I guess it works here.

As noted elsewhere:  IRQF_DISABLED will probably be needed.

> +		if (rc) {
> +			free_irq(ms->irq0, ms);
> +			free_irq(ms->irq1, ms);
> +			ms->irq0 = ms->irq1 = NO_IRQ;
> +			dev_info(&op->dev, "using polled mode\n");
> +		}
> +	} else {
> +		/* operate in polled mode */
> +		ms->irq0 = ms->irq1 = NO_IRQ;
> +		dev_info(&op->dev, "using polled mode\n");

irq0 = 0;
irq1 = 0;

> +	}
> +
> +	/* Create SysFS files */
> +	rc = device_create_file(&ms->master->dev, &dev_attr_msg_count);
> +	rc |= device_create_file(&ms->master->dev, &dev_attr_byte_count);
> +	rc |= device_create_file(&ms->master->dev, &dev_attr_wcol_count);
> +	rc |= device_create_file(&ms->master->dev, &dev_attr_wcol_ticks);
> +	rc |= device_create_file(&ms->master->dev, &dev_attr_modf_count);

The minimalist in me wonders if those device files should exist,
or at least be moved to debugfs.

> +	if (rc)
> +		dev_info(&ms->master->dev, "error creating sysfs files\n");

The practical person in me notes that this continues after an otherwise
correct setup, but then returns a failure code from probe().  Which is
clearly a bug ...

> +
> +	dev_info(&ms->master->dev, "registered MPC5200 SPI bus\n");
> +
> +	of_register_spi_devices(master, op->node);
> +
> +	return rc;
> +
> + err_register:
> +	dev_err(&ms->master->dev, "initialization failed\n");
> +	spi_master_put(master);
> +	return rc;
> +}
> +
> +static void __devexit mpc52xx_spi_of_remove(struct of_device *op)
> +{
> +	struct spi_master *master = dev_get_drvdata(&op->dev);
> +	struct mpc52xx_spi *ms = spi_master_get_devdata(master);
> +
> +	device_remove_file(&ms->master->dev, &dev_attr_msg_count);
> +	device_remove_file(&ms->master->dev, &dev_attr_byte_count);
> +	device_remove_file(&ms->master->dev, &dev_attr_wcol_count);
> +	device_remove_file(&ms->master->dev, &dev_attr_wcol_ticks);
> +	device_remove_file(&ms->master->dev, &dev_attr_modf_count);
> +
> +	free_irq(ms->irq0, ms);
> +	free_irq(ms->irq1, ms);
> +
> +	spi_unregister_master(master);
> +	spi_master_put(master);
> +	iounmap(ms->regs);
> +}
> +
> +static struct of_device_id mpc52xx_spi_of_match[] __devinitdata = {
> +	{ .compatible = "fsl,mpc5200-spi", },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, mpc52xx_psc_spi_of_match);
> +
> +static struct of_platform_driver mpc52xx_spi_of_driver = {
> +	.owner = THIS_MODULE,
> +	.name = "mpc52xx-spi",
> +	.match_table = mpc52xx_spi_of_match,
> +	.probe = mpc52xx_spi_of_probe,
> +	.remove = __exit_p(mpc52xx_spi_of_remove),
> +};
> +
> +static int __init mpc52xx_spi_init(void)
> +{
> +	return of_register_platform_driver(&mpc52xx_spi_of_driver);
> +}
> +module_init(mpc52xx_spi_init);
> +
> +static void __exit mpc52xx_spi_exit(void)
> +{
> +	of_unregister_platform_driver(&mpc52xx_spi_of_driver);
> +}
> +module_exit(mpc52xx_spi_exit);
> +
> diff --git a/include/linux/spi/mpc52xx_spi.h b/include/linux/spi/mpc52xx_spi.h
> new file mode 100644
> index 0000000..d1004cf
> --- /dev/null
> +++ b/include/linux/spi/mpc52xx_spi.h
> @@ -0,0 +1,10 @@
> +
> +#ifndef INCLUDE_MPC5200_SPI_H
> +#define INCLUDE_MPC5200_SPI_H
> +
> +extern void mpc52xx_spi_set_premessage_hook(struct spi_master *master,
> +					    void (*hook)(struct spi_message *m,
> +							 void *context),
> +					    void *hook_context);
> +
> +#endif
>