linux-kernel - Re: [PATCH RFC 01/11 v4] gpio: Add a block GPIO API to gpiolib

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Date:	Tue, 16 Oct 2012 11:18:15 +1100
From:	Ryan Mallon <rmallon@...il.com>
To:	Roland Stigge <stigge@...com.de>
CC:	grant.likely@...retlab.ca, linus.walleij@...aro.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	w.sang@...gutronix.de, jbe@...gutronix.de, plagnioj@...osoft.com,
	highguy@...il.com, broonie@...nsource.wolfsonmicro.com,
	daniel-gl@....net, gregkh@...uxfoundation.org
Subject: Re: [PATCH RFC 01/11 v4] gpio: Add a block GPIO API to gpiolib

On 16/10/12 10:31, Roland Stigge wrote:
> The recurring task of providing simultaneous access to GPIO lines (especially
> for bit banging protocols) needs an appropriate API.
> 
> This patch adds a kernel internal "Block GPIO" API that enables simultaneous
> access to several GPIOs. This is done by abstracting GPIOs to an n-bit word:
> Once requested, it provides access to a group of GPIOs which can range over
> multiple GPIO chips.
> 
> Signed-off-by: Roland Stigge <stigge@...com.de>
> ---

<snip>

> +This creates a new block of GPIOs as a list of GPIO numbers with the specified
> +size which are accessible via the returned struct gpio_block and the accessor
> +functions described below. Please note that you need to request the GPIOs
> +separately via gpio_request(). An arbitrary list of globally valid GPIOs can be
> +specified, even ranging over several gpio_chips. Actual handling of I/O
> +operations will be done on a best effort base, i.e. simultaneous I/O only where
> +possible by hardware and implemented in the respective GPIO driver. The number
> +of GPIOs in one block is limited to 32 on a 32 bit system, and 64 on a 64 bit
> +system. However, several blocks can be defined at once.

This should probably say that the number of gpios in a block is limited
to sizeof(unsigned long) or BITS_PER_LONG. I think sizeof(unsigned long)
== 8 on some 32 bit architectures.

~Ryan

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