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

[Shawn Guo]

Hi Uwe,

On Wed, Dec 29, 2010 at 12:22:08PM +0100, Uwe Kleine-König wrote:
> Hello,
> 
> 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?)
> For 2. there is no check for HW_OCOTP_CTRL_ERROR which is not OK i
> guess?!
> 
Will add the check. Thanks.

> (Independant of that, shouldn't the list use BM_ prefixes as you did in
> the code?)
> 
Document description uses register name followed by bit-field name
to mean the bit.

> > +
> > +	/* approximately wait 32 hclk cycles */
> > +	udelay(1);
> > +
> > +	/* poll BUSY bit becoming cleared */
> > +	while ((__raw_readl(ocotp_base) & BM_OCOTP_CTRL_BUSY) && --timeout)
> > +		/* nothing */;
> > +
> > +	if (unlikely(!timeout))
> > +		goto error;
> And I think you should recheck for BM_OCOTP_CTRL_RD_BANK_OPEN here (step
> 4 from the reference manual).
> 
The RM says:

Poll for HW_OCOTP_CTRL_BUSY clear. When HW_OCOTP_CTRL_BUSY is clear
and HW_OCOTP_CTRL_RD_BANK_OPEN is set, read the data from the
appropriate memory-mapped address.

My understanding is we only need to poll busy bit clear. And the
second sentence just tells that read operation should be working
when bit busy clear and rd_bank_open set, which has been done
in step 3. I also consulted the designer and was told that only
busy clear polling is needed.

-- 
Regards,
Shawn