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From: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
To: dedekind1@gmail.com
Subject: Re: [PATCH v3.4-rc3] MTD: NAND: ams-delta: Fix request_mem_region()
 failure
Date: Wed, 25 Apr 2012 19:01:14 +0200
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Cc: Tony Lindgren <tony@atomide.com>,
 Artem Bityutskiy <Artem.Bityutskiy@linux.intel.com>,
 linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org,
 linux-omap@vger.kernel.org, David Woodhouse <dwmw2@infradead.org>
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Dnia =C5=9Broda, 25 kwietnia 2012 18:13:38 Artem Bityutskiy pisze:
> On Tue, 2012-04-17 at 15:49 +0200, Janusz Krzysztofik wrote:
> > A call to request_mem_region() has been introduced in the omap-gpio=

> > driver recently (commit 96751fcbe5438e95514b025e9cee7a6d38038f40,
> > "gpio/omap: Use devm_ API and add request_mem_region"). This change=

> > prevented the Amstrad Delta NAND driver, which was doing the same i=
n
> > order to take control over OMAP MPU I/O lines that the NAND device=20=

hangs
> > off, from loading successfully.
> >=20
> > There is another driver, omap-keypad, which also manipulates OMAP=20=

MPUIO
> > registers, but has never been calling request_mem_region() on=20
startup,
> > so it's not affected by the change in the gpio-omap and works=20
correctly.
> >=20
> > Drop request_mem_region() call and related bits from ams-delta NAND=

> > driver.
> >=20
> > Created and tested against linux-3.4-rc3.
> >=20
> > Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
>=20
> How about race conditions? Where is the guarantee that these 2 driver=
s
> won't affect each other when doing I/O at the same time to the same H=
W
> resources?

Both drivers use separate subsets of registers that belong to the OMAP1=
=20
MPU I/O device, but are used for controlling different sets of I/O pins=
.=20
The NAND driver reads/writes the folowing registers:
- OMAP_MPUIO_INPUT_LATCH,
- OMAP_MPUIO_OUTPUT,
- OMAP_MPUIO_IO_CNTL,
while the keypad driver - the following:
- OMAP_MPUIO_KBR_LATCH,
- OMAP_MPUIO_KBC,
- OMAP_MPUIO_KBD_MASKIT
- OMAP_MPUIO_GPIO_DEBOUNCING.
Both subsets are non-overlapping, and we rely on the drivers being free=
=20
of bugs and doing their job correctly, not stepping on each others'=20
feet, I guess.

Thanks,
Janusz