linux-kernel - Re: [PATCH RESEND 0/6 v10] gpio: Add block GPIO

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Date:	Mon, 17 Dec 2012 14:32:33 +0100
From:	Roland Stigge <stigge@...com.de>
To:	Wolfgang Grandegger <wg@...ndegger.com>
CC:	rmallon@...il.com, gregkh@...uxfoundation.org,
	linus.walleij@...aro.org, broonie@...nsource.wolfsonmicro.com,
	linux-kernel@...r.kernel.org, w.sang@...gutronix.de,
	grant.likely@...retlab.ca, daniel-gl@....net, sr@...x.de,
	plagnioj@...osoft.com, linux-arm-kernel@...ts.infradead.org,
	highguy@...il.com
Subject: Re: [PATCH RESEND 0/6 v10] gpio: Add block GPIO

On 12/17/2012 12:51 PM, Wolfgang Grandegger wrote:
>>> Without having an AT91 available right now, I guess the hardware
>>> interface of this GPIO chip is different from the GPIO block API. While
>>> the hardware has clear and set registers, the val parameter of
>>> at91_gpiolib_set_block() should be interpreted as the actual output
>>> values. See lpc32xx_gpo_set_block() for an example for handling set and
>>> clear registers like this: First, set_bits and clear_bits words are
>>> calculated from mask and val parameters, and finally written to the
>>> respective hardware registers.
>>>
>>> Note that one .set_block() can result in writing both the set and clear
>>> registers of the hardware when val contains both 0s and 1s in
>>> respectively masked positions.
>>
>> Oops, I obviously did not test GPIO block write. The patch below does
>> work now. Feel free to add it to the next version of your series.
> 
> The patch lacks an important fix, sorry. Please consider the updated
> patch below.

Thanks!

And I guess Russell is right: If possible, we should write outputs
simultaneously via ODSR (plus OWER/OWDR/OWSR) instead of separate set/clear.

I wonder if we need to save/restore the state of OWSR at every write
operation or if we need/can cache it. Assuming that block GPIO are the
only code in the kernel that manipulates ODSR.

Further: Can we include this patch for arch/arm/mach-at91 via the gpio
subsystem or does it need to go separately via arm-soc.git?

Thanks,

Roland
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