netdev - Re: [PATCH v3 08/10] ARM: mxs: add ocotp read function

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Date:	Wed, 5 Jan 2011 17:44:09 +0100
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Jamie Iles <jamie@...ieiles.com>
Cc:	Shawn Guo <shawn.guo@...escale.com>, gerg@...pgear.com,
	B32542@...escale.com, netdev@...r.kernel.org,
	s.hauer@...gutronix.de, baruch@...s.co.il, w.sang@...gutronix.de,
	r64343@...escale.com, eric@...rea.com, bryan.wu@...onical.com,
	davem@...emloft.net, linux-arm-kernel@...ts.infradead.org,
	lw@...o-electronics.de
Subject: Re: [PATCH v3 08/10] ARM: mxs: add ocotp read function

Hello Jamie,

On Wed, Jan 05, 2011 at 04:16:46PM +0000, Jamie Iles wrote:
> On Wed, Jan 05, 2011 at 10:07:35PM +0800, Shawn Guo wrote:
> > Signed-off-by: Shawn Guo <shawn.guo@...escale.com>
> > ---
> > 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/ocotp.c b/arch/arm/mach-mxs/ocotp.c
> > new file mode 100644
> > index 0000000..902ef59
> > --- /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);
> > +
> > +	/* check both BUSY and ERROR cleared */
> > +	while ((__raw_readl(ocotp_base) &
> > +		(BM_OCOTP_CTRL_BUSY | BM_OCOTP_CTRL_ERROR)) && --timeout)
> > +		/* nothing */;
> 
> Is it worth using cpu_relax() in these polling loops?
I don't know what cpu_relax does for other platforms, but on ARM it's
just a memory barrier which AFAICT doesn't help here at all (which
doesn't need to be correct).  Why do you think it would be better?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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