linux-kernel - Re: [PATCH 6/6 v14] gpio: Add block gpio to several gpio drivers

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Message-ID: <20130124121726.GQ4955@opensource.wolfsonmicro.com>
Date:	Thu, 24 Jan 2013 20:17:30 +0800
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Stijn Devriendt <highguy@...il.com>
Cc:	Roland Stigge <stigge@...com.de>, gregkh@...uxfoundation.org,
	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,
	daniel-gl@....net, rmallon@...il.com, sr@...x.de,
	wg@...ndegger.com, mark.rutland@....com, nicolas.ferre@...el.com
Subject: Re: [PATCH 6/6 v14] gpio: Add block gpio to several gpio drivers

On Thu, Jan 24, 2013 at 01:02:38PM +0100, Stijn Devriendt wrote:

> As a fictive example, consider the i2c-bitbang driver, which you could optimize
> by using block-gpio with sda/scl in a single block. By offering the
> block-gpio API
> even when you cannot set all bits at once, you could cause timing issues.
> You might be toggling the clock line before pushing out data, for example.

> The same holds below, for a driver that has separate hi/lo bits.

If there's a strict ordering requirement on updates then I would expect
a user to explictly code that in hardware otherwise there may be
hardware level issues with unpredictable results; besides in general it
seems silly to force users to open code both versions if they don't want
to rely on this API.

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