Subject: Re: [patch 3/3] ps3: FLASH ROM Storage Driver

From: Andrew Morton <[email-masked]>
Date: Wed, 18 Jul 2007 16:52:22 -0700

On Mon, 16 Jul 2007 18:15:42 +0200
Geert Uytterhoeven <[email-masked]> wrote:

> From: Geert Uytterhoeven <[email-masked]>
> 
> Add a FLASH ROM Storage Driver for the PS3:
>   - Implemented as a misc character device driver
>   - Uses a fixed 256 KiB buffer allocated from boot memory as the hypervisor
>     requires the writing of aligned 256 KiB blocks
> 
> --- /dev/null
> +++ b/drivers/char/ps3flash.c
> @@ -0,0 +1,429 @@
> +/*
> + * PS3 FLASH ROM Storage Driver
> + *
> + * Copyright (C) 2007 Sony Computer Entertainment Inc.
> + * Copyright 2007 Sony Corp.
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License as published
> + * by the Free Software Foundation; version 2 of the License.
> + *
> + * This program is distributed in the hope that it will be useful, but
> + * WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License along
> + * with this program; if not, write to the Free Software Foundation, Inc.,
> + * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
> + */
> +
> +#include <linux/fs.h>
> +#include <linux/miscdevice.h>
> +#include <linux/uaccess.h>
> +
> +#include <asm/lv1call.h>
> +#include <asm/ps3stor.h>
> +
> +
> +#define DEVICE_NAME		"ps3flash"
> +
> +#define FLASH_BLOCK_SIZE	(256*1024)
> +
> +
> +struct ps3flash_private {
> +	struct mutex mutex;	/* Bounce buffer mutex */
> +};
> +#define ps3flash_priv(dev)	((dev)->sbd.core.driver_data)

bzzzt!

> +static loff_t ps3flash_llseek(struct file *file, loff_t offset, int origin)
> +{
> +	struct ps3_storage_device *dev = ps3flash_dev;
> +	u64 size = dev->regions[dev->region_idx].size*dev->blk_size;
> +
> +	switch (origin) {
> +	case 1:
> +		offset += file->f_pos;
> +		break;
> +	case 2:
> +		offset += size;
> +		break;
> +	}
> +	if (offset < 0)
> +		return -EINVAL;
> +
> +	file->f_pos = offset;
> +	return file->f_pos;
> +}

lseek implementations usually need locking.  file->f_mapping->host->i_mutex
would be typical.

That locking mostly protects 64-bit f_pos on 32-bit architectures so you
can perahps kinda get away with it here.  However the code is a bit racy
even on 64-bit, for silly userspace.

That being said, I'd have thought that you could use one of our many
generic lseek library fucntions here, or even an newly-exported
block_llseek().  That assumes that i_size is correct, which I trust is the
case.

> +static ssize_t ps3flash_read(struct file *file, char __user *buf, size_t count,
> +			     loff_t *pos)
> +{
> +	struct ps3_storage_device *dev = ps3flash_dev;
> +	struct ps3flash_private *priv = ps3flash_priv(dev);
> +	u64 size, start_sector, end_sector, offset;
> +	ssize_t sectors_read;
> +	size_t remaining, n;
> +
> +	dev_dbg(&dev->sbd.core,
> +		"%s:%u: Reading %zu bytes at position %lld to user 0x%p\n",
> +		__func__, __LINE__, count, *pos, buf);
> +
> +	size = dev->regions[dev->region_idx].size*dev->blk_size;
> +	if (*pos >= size || !count)
> +		return 0;
> +
> +	if (*pos+count > size) {
> +		dev_dbg(&dev->sbd.core,
> +			"%s:%u Truncating count from %zu to %llu\n", __func__,
> +			__LINE__, count, size - *pos);
> +		count = size - *pos;
> +	}
> +
> +	start_sector = do_div_llr(*pos, dev->blk_size, &offset);
> +	end_sector = DIV_ROUND_UP(*pos+count, dev->blk_size);
> +
> +	remaining = count;
> +	do {
> +		mutex_lock(&priv->mutex);
> +
> +		sectors_read = ps3flash_read_sectors(dev, start_sector,
> +						     end_sector-start_sector,
> +						     0);
> +		if (sectors_read < 0) {
> +			mutex_unlock(&priv->mutex);
> +			return sectors_read;
> +		}
> +
> +		n = min(remaining, sectors_read*dev->blk_size-offset);
> +		dev_dbg(&dev->sbd.core,
> +			"%s:%u: copy %lu bytes from 0x%p to user 0x%p\n",
> +			__func__, __LINE__, n, dev->bounce_buf+offset, buf);
> +		if (copy_to_user(buf, dev->bounce_buf+offset, n)) {
> +			mutex_unlock(&priv->mutex);
> +			return -EFAULT;
> +		}
> +
> +		mutex_unlock(&priv->mutex);
> +
> +		*pos += n;
> +		buf += n;
> +		remaining -= n;
> +		start_sector += sectors_read;
> +		offset = 0;
> +	} while (remaining > 0);
> +
> +	return count;
> +}

There are several nasty deeply-embedded return points in this function.

> +static ssize_t ps3flash_write(struct file *file, const char __user *buf,
> +			      size_t count, loff_t *pos)
> +{
> +	struct ps3_storage_device *dev = ps3flash_dev;
> +	struct ps3flash_private *priv = ps3flash_priv(dev);
> +	u64 size, chunk_sectors, start_write_sector, end_write_sector,
> +	    end_read_sector, start_read_sector, head, tail, offset;
> +	ssize_t res;
> +	size_t remaining, n;
> +	unsigned int sec_off;
> +
> +	dev_dbg(&dev->sbd.core,
> +		"%s:%u: Writing %zu bytes at position %lld from user 0x%p\n",
> +		__func__, __LINE__, count, *pos, buf);
> +
> +	size = dev->regions[dev->region_idx].size*dev->blk_size;
> +	if (*pos >= size || !count)
> +		return 0;
> +
> +	if (*pos+count > size) {

checkpatch missed stuff here.

> +		dev_dbg(&dev->sbd.core,
> +			"%s:%u Truncating count from %zu to %llu\n", __func__,
> +			__LINE__, count, size - *pos);
> +		count = size - *pos;
> +	}
> +
> +	chunk_sectors = dev->bounce_size / dev->blk_size;
> +
> +	start_write_sector = do_div_llr(*pos, dev->bounce_size, &offset) *
> +			     chunk_sectors;

It's strange to see a do_div_llr() in the middle of all this 64-bit-only
code.  Could use / and %?

> +	end_write_sector = DIV_ROUND_UP(*pos+count, dev->bounce_size) *
> +			   chunk_sectors;
> +
> +	end_read_sector = DIV_ROUND_UP(*pos, dev->blk_size);
> +	start_read_sector = (*pos+count) / dev->blk_size;
> +
> +	/*
> +	 * As we have to write in 256 KiB chunks, while we can read in blk_size
> +	 * (usually 512 bytes) chunks, we perform the following steps:
> +	 *   1. Read from start_write_sector to end_read_sector ("head")
> +	 *   2. Read from start_read_sector to end_write_sector ("tail")
> +	 *   3. Copy data to buffer
> +	 *   4. Write from start_write_sector to end_write_sector
> +	 * All of this is complicated by using only one 256 KiB bounce buffer.
> +	 */
> +
> +	head = end_read_sector-start_write_sector;
> +	tail = end_write_sector-start_read_sector;

checkpatch missed this too.

> +	remaining = count;
> +	do {
> +		mutex_lock(&priv->mutex);
> +
> +		if (end_read_sector >= start_read_sector) {
> +			/* Merge head and tail */
> +			dev_dbg(&dev->sbd.core,
> +				"Merged head and tail: %lu sectors at %lu\n",
> +				chunk_sectors, start_write_sector);
> +			res = ps3flash_read_sectors(dev, start_write_sector,
> +						    chunk_sectors, 0);
> +			if (res < 0)
> +				goto fail;
> +		} else {
> +			if (head) {
> +				/* Read head */
> +				dev_dbg(&dev->sbd.core,
> +					"head: %lu sectors at %lu\n", head,
> +					start_write_sector);
> +				res = ps3flash_read_sectors(dev,
> +							    start_write_sector,
> +							    head, 0);
> +				if (res < 0)
> +					goto fail;
> +			}
> +			if (start_read_sector <
> +			    start_write_sector+chunk_sectors) {
> +				/* Read tail */
> +				dev_dbg(&dev->sbd.core,
> +					"tail: %lu sectors at %lu\n", tail,
> +					start_read_sector);
> +				sec_off = start_read_sector-start_write_sector;
> +				res = ps3flash_read_sectors(dev,
> +							    start_read_sector,
> +							    tail, sec_off);
> +				if (res < 0)
> +					goto fail;
> +			}
> +		}
> +
> +		n = min(remaining, dev->bounce_size-offset);
> +		dev_dbg(&dev->sbd.core,
> +			"%s:%u: copy %lu bytes from user 0x%p to 0x%p\n",
> +			__func__, __LINE__, n, buf, dev->bounce_buf+offset);
> +		if (copy_from_user(dev->bounce_buf+offset, buf, n)) {
> +			res = -EFAULT;
> +			goto fail;
> +		}
> +
> +		res = ps3flash_write_chunk(dev, start_write_sector);
> +		if (res < 0)
> +			goto fail;
> +
> +		mutex_unlock(&priv->mutex);
> +
> +		*pos += n;
> +		buf += n;
> +		remaining -= n;
> +		start_write_sector += chunk_sectors;
> +		head = 0;
> +		offset = 0;
> +	} while (remaining > 0);
> +
> +	return count;
> +
> +fail:
> +	mutex_unlock(&priv->mutex);
> +	return res;
> +}
>
> ...
>
> +static int __devinit ps3flash_probe(struct ps3_system_bus_device *_dev)
> +{
> +	struct ps3_storage_device *dev = to_ps3_storage_device(&_dev->core);
> +	struct ps3flash_private *priv;
> +	int error;
> +	unsigned long tmp;
> +
> +	tmp = dev->regions[dev->region_idx].start*dev->blk_size;
> +	if (tmp % FLASH_BLOCK_SIZE) {
> +		dev_err(&dev->sbd.core,
> +			"%s:%u region start %lu is not aligned\n", __func__,
> +			__LINE__, tmp);
> +		return -EINVAL;
> +	}
> +	tmp = dev->regions[dev->region_idx].size*dev->blk_size;
> +	if (tmp % FLASH_BLOCK_SIZE) {
> +		dev_err(&dev->sbd.core,
> +			"%s:%u region size %lu is not aligned\n", __func__,
> +			__LINE__, tmp);
> +		return -EINVAL;
> +	}
> +
> +	/* use static buffer, kmalloc cannot allocate 256 KiB */
> +	if (!ps3flash_bounce_buffer.address)
> +		return -ENODEV;
> +
> +	if (ps3flash_dev) {
> +		dev_err(&dev->sbd.core,
> +			"Only one FLASH device is supported\n");
> +		return -EBUSY;
> +	}
> +
> +	ps3flash_dev = dev;
> +
> +	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
> +	if (!priv) {
> +		error = -ENOMEM;
> +		goto fail;
> +	}
> +
> +	ps3flash_priv(dev) = priv;
> +	mutex_init(&priv->mutex);
> +
> +	dev->bounce_size = ps3flash_bounce_buffer.size;
> +	dev->bounce_buf = ps3flash_bounce_buffer.address;
> +
> +	error = ps3stor_setup(dev, ps3flash_interrupt);
> +	if (error)
> +		goto fail_free_priv;
> +
> +	ps3flash_misc.parent = &dev->sbd.core;
> +	error = misc_register(&ps3flash_misc);
> +	if (error) {
> +		dev_err(&dev->sbd.core, "%s:%u: misc_register failed %d\n",
> +			__func__, __LINE__, error);
> +		goto fail_teardown;
> +	}
> +
> +	dev_info(&dev->sbd.core, "%s:%u: registered misc device %d\n",
> +		 __func__, __LINE__, ps3flash_misc.minor);
> +	return 0;
> +
> +fail_teardown:
> +	ps3stor_teardown(dev);
> +fail_free_priv:
> +	kfree(priv);
> +	ps3flash_priv(dev) = NULL;
> +fail:
> +	ps3flash_dev = NULL;
> +	return error;
> +}
> +