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

[u.kleine-koenig@pengutronix.de (Uwe Kleine-König)]

Hello Shawn,

On Thu, Dec 30, 2010 at 04:41:40PM +0800, Shawn Guo wrote:
> On Wed, Dec 29, 2010 at 12:22:08PM +0100, Uwe Kleine-K?nig wrote:
> > On Tue, Dec 28, 2010 at 10:55:53PM +0800, Shawn Guo wrote:
> > > diff --git a/arch/arm/mach-mxs/ocotp.c b/arch/arm/mach-mxs/ocotp.c
> > > new file mode 100644
> > > index 0000000..24457d7
> > > --- /dev/null
> > > +++ b/arch/arm/mach-mxs/ocotp.c
> > > @@ -0,0 +1,52 @@
> > > +/*
> > > + * 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 <mach/mxs.h>
> > > +
> > > +#define BM_OCOTP_CTRL_RD_BANK_OPEN	(1 << 12)
> > > +#define BM_OCOTP_CTRL_BUSY		(1 << 8)
> > > +
> > > +int mxs_read_ocotp(int offset, int count, u32 *values)
> > > +{
> > > +	void __iomem *ocotp_base = MXS_IO_ADDRESS(MXS_OCOTP_BASE_ADDR);
> > > +	int i, timeout = 0x400;
> > > +
> > > +	/* open OCOTP banks for read */
> > > +	__mxs_setl(BM_OCOTP_CTRL_RD_BANK_OPEN, ocotp_base);
> > The reference manual specifies:
> > 	1. Program the HCLK to a frequency up to the maximum allowable HCLK
> > 	   frequency. [...]
> > 	2. Check that HW_OCOTP_CTRL_BUSY and HW_OCOTP_CTRL_ERROR are clear.
> > 	3. Set HW_OCOTP_CTRL_RD_BANK_OPEN. [...]
> > 
> > 1. isn't done (which is probably OK, or should it aquire a clk?)
> ocotp needs clk_h, which must be on when system is running.
maybe add a comment?  "clk_enable(clk_h) can be skipped as it must be on
anyhow because ..." or similar?  It's always good to document implicit
assumptions.

> > For 2. there is no check for HW_OCOTP_CTRL_ERROR which is not OK i
> > guess?!
> > 
> How does the new code look to you?
> 
> 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 i, timeout = 0x400;
i should be size_t, too

> 
> 	mutex_lock(&ocotp_mutex);
> 
> 	/* clear ERROR bit anyway */
anyway?  Better?: "try to clear ERROR bit"

> 	__mxs_clrl(BM_OCOTP_CTRL_ERROR, ocotp_base);
> 
> 	/* check both BUSY and ERROR cleared */
> 	while ((__raw_readl(ocotp_base) &
> 		(BM_OCOTP_CTRL_BUSY | BM_OCOTP_CTRL_ERROR)) && --timeout)
> 		/* nothing */;
> 
> 	if (unlikely(!timeout))
> 		goto error;
This goto and some more leave the critical section without unlocking the
mutex.

> 
> 	/* 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)
> 		/* nothing */;
> 
> 	if (unlikely(!timeout))
> 		goto error;
> 
> 	for (i = 0; i < count; i++, offset += 4)
> 		*values++ = __raw_readl(ocotp_base + offset);
> 
> 	/* close banks for power saving */
> 	__mxs_clrl(BM_OCOTP_CTRL_RD_BANK_OPEN, ocotp_base);
> 
> 	mutex_unlock(&ocotp_mutex);
> 
> 	return 0;
> 
> error:
> 	pr_err("%s: timeout in reading OCOTP\n", __func__);
> 	return -ETIMEDOUT;
> }
I think it's OK then.  One optimisation that comes to my mind is to make
BM_OCOTP_CTRL_RD_BANK_OPEN a clk (that can depend on clk_h).  This would
allow for multiple readers, but I think it's not worth the effort.

Best regards
Uwe

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