Subject: Re: [PATCH v4 08/10] ARM: mxs: add ocotp read function

From: Shawn Guo <[email-masked]>
Date: Thu, 13 Jan 2011 09:55:46 +0800

On Wed, Jan 12, 2011 at 05:01:06PM +0100, Uwe Kleine-König wrote:
> Hello Sascha,
> 
> On Wed, Jan 12, 2011 at 03:50:36PM +0100, Sascha Hauer wrote:
> > On Wed, Jan 12, 2011 at 02:47:12PM +0800, Shawn Guo wrote:
> > > On Tue, Jan 11, 2011 at 02:31:37PM +0100, Sascha Hauer wrote:
> > > > On Thu, Jan 06, 2011 at 03:13:16PM +0800, Shawn Guo wrote:
> > > > > Signed-off-by: Shawn Guo <[email-masked]>
> > > > > ---
> > > > > Changes for v4:
> > > > >  - Call cpu_relax() during polling
> > > > > 
> > > > > Changes for v2:
> > > > >  - Add mutex locking for mxs_read_ocotp()
> > > > >  - Use type size_t for count and i
> > > > >  - Add comment for clk_enable/disable skipping
> > > > >  - Add ERROR bit clearing and polling step
> > > > > 
> > > > >  arch/arm/mach-mxs/Makefile              |    2 +-
> > > > >  arch/arm/mach-mxs/include/mach/common.h |    1 +
> > > > >  arch/arm/mach-mxs/ocotp.c               |   79 +++++++++++++++++++++++++++++++
> > > > >  3 files changed, 81 insertions(+), 1 deletions(-)
> > > > >  create mode 100644 arch/arm/mach-mxs/ocotp.c
> > > > > 
> > > > > diff --git a/arch/arm/mach-mxs/Makefile b/arch/arm/mach-mxs/Makefile
> > > > > index 39d3f9c..f23ebbd 100644
> > > > > --- a/arch/arm/mach-mxs/Makefile
> > > > > +++ b/arch/arm/mach-mxs/Makefile
> > > > > @@ -1,5 +1,5 @@
> > > > >  # Common support
> > > > > -obj-y := clock.o devices.o gpio.o icoll.o iomux.o system.o timer.o
> > > > > +obj-y := clock.o devices.o gpio.o icoll.o iomux.o ocotp.o system.o timer.o
> > > > >  
> > > > >  obj-$(CONFIG_SOC_IMX23) += clock-mx23.o mm-mx23.o
> > > > >  obj-$(CONFIG_SOC_IMX28) += clock-mx28.o mm-mx28.o
> > > > > diff --git a/arch/arm/mach-mxs/include/mach/common.h b/arch/arm/mach-mxs/include/mach/common.h
> > > > > index 59133eb..cf02552 100644
> > > > > --- a/arch/arm/mach-mxs/include/mach/common.h
> > > > > +++ b/arch/arm/mach-mxs/include/mach/common.h
> > > > > @@ -13,6 +13,7 @@
> > > > >  
> > > > >  struct clk;
> > > > >  
> > > > > +extern int mxs_read_ocotp(int offset, int count, u32 *values);
> > > > >  extern int mxs_reset_block(void __iomem *);
> > > > >  extern void mxs_timer_init(struct clk *, int);
> > > > >  
> > > > > diff --git a/arch/arm/mach-mxs/ocotp.c b/arch/arm/mach-mxs/ocotp.c
> > > > > new file mode 100644
> > > > > index 0000000..e2d39aa
> > > > > --- /dev/null
> > > > > +++ b/arch/arm/mach-mxs/ocotp.c
> > > > > @@ -0,0 +1,79 @@
> > > > > +/*
> > > > > + * Copyright 2010 Freescale Semiconductor, Inc. All Rights Reserved.
> > > > > + *
> > > > > + * 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; either version 2 of the License, or
> > > > > + * (at your option) any later version.
> > > > > + *
> > > > > + * 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.
> > > > > + */
> > > > > +
> > > > > +#include <linux/delay.h>
> > > > > +#include <linux/err.h>
> > > > > +#include <linux/mutex.h>
> > > > > +
> > > > > +#include <mach/mxs.h>
> > > > > +
> > > > > +#define BM_OCOTP_CTRL_BUSY		(1 << 8)
> > > > > +#define BM_OCOTP_CTRL_ERROR		(1 << 9)
> > > > > +#define BM_OCOTP_CTRL_RD_BANK_OPEN	(1 << 12)
> > > > > +
> > > > > +static DEFINE_MUTEX(ocotp_mutex);
> > > > > +
> > > > > +int mxs_read_ocotp(unsigned offset, size_t count, u32 *values)
> > > > > +{
> > > > > +	void __iomem *ocotp_base = MXS_IO_ADDRESS(MXS_OCOTP_BASE_ADDR);
> > > > > +	int timeout = 0x400;
> > > > > +	size_t i;
> > > > > +
> > > > > +	mutex_lock(&ocotp_mutex);
> > > > > +
> > > > > +	/*
> > > > > +	 * clk_enable(hbus_clk) for ocotp can be skipped
> > > > > +	 * as it must be on when system is running.
> > > > > +	 */
> > > > > +
> > > > > +	/* try to clear ERROR bit */
> > > > > +	__mxs_clrl(BM_OCOTP_CTRL_ERROR, ocotp_base);
> > > > 
> > > > This operation does not try to clear the error bit but actually clears
> > > > it...
> > > > 
> > > > > +
> > > > > +	/* check both BUSY and ERROR cleared */
> > > > > +	while ((__raw_readl(ocotp_base) &
> > > > > +		(BM_OCOTP_CTRL_BUSY | BM_OCOTP_CTRL_ERROR)) && --timeout)
> > > > > +		cpu_relax();
> > > > 
> > > > ...which means you do not have to poll the error bit here...
> > > > 
> > > > > +
> > > > > +	if (unlikely(!timeout))
> > > > > +		goto error_unlock;
> > > > > +
> > > > > +	/* open OCOTP banks for read */
> > > > > +	__mxs_setl(BM_OCOTP_CTRL_RD_BANK_OPEN, ocotp_base);
> > > > > +
> > > > > +	/* approximately wait 32 hclk cycles */
> > > > > +	udelay(1);
> > > > > +
> > > > > +	/* poll BUSY bit becoming cleared */
> > > > > +	timeout = 0x400;
> > > > > +	while ((__raw_readl(ocotp_base) & BM_OCOTP_CTRL_BUSY) && --timeout)
> > > > > +		cpu_relax();
> > > > 
> > > > ...which means you can factor out a ocotp_wait_busy function and let the
> > > > code speak instead of the comments.
> > > > 
> > > > > +
> > > > > +	if (unlikely(!timeout))
> > > > > +		goto error_unlock;
> > > > > +
> > > > > +	for (i = 0; i < count; i++, offset += 4)
> > > > > +		*values++ = __raw_readl(ocotp_base + offset);
> > > > 
> > > > The registers in the ocotp are 16 byte aligned. Does it really make
> > > > sense to provide a function allowing to read the gaps between the
> > > > registers?
> > > > 
> > > Good catch.  The count was added to ease the consecutive otp word
> > > reading, as there is bank open/close cost for otp read.  What about
> > > the following changes?
> > > 
> > > int mxs_read_ocotp(unsigned offset, size_t otp_word_cnt, u32 *values)
> > > {
> > > 	......
> > > 
> > > 	for (i = 0; i < otp_word_cnt; i++, offset += 0x10)
> > > 		*values++ = __raw_readl(ocotp_base + offset);
> > > 
> > > 	......
> > > }
> > 
> > I would rather make a function like this:
> > 
> > static u32 ocotp[0x27];
> > 
> > const u32 *mxs_get_ocotp(void)
> > {
> > 	static int once = 0;
> > 
> > 	if (once)
> > 		return ocotp
> > 
> > 	/* bank open */
> > 
> > 	for (i = 0; i < 0x27; i++)
> > 		ocotp[i] = readl(ocotp_base + 0x20 + i * 0x10)
> > 
> > 	/* bank_close */
> > 
> > 	once = 1;
> > 
> > 	return ocotp;
> which is save on UP when it's not called from irq context.
> 
> Additionally I suggest a #define for 0x27 and 0x20.
> 

So I will keep the mutex and not read SRK bits.

Thanks for the comments.

-- 
Regards,
Shawn