linux-kernel - RE: [PATCH v2] pinctrl: at91-pio4: implement .get_multiple and .set

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Date:   Fri, 6 Sep 2019 09:05:36 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alexandre Belloni' <alexandre.belloni@...tlin.com>,
        Linus Walleij <linus.walleij@...aro.org>
CC:     Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        "Claudiu.Beznea@...rochip.com" <Claudiu.Beznea@...rochip.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] pinctrl: at91-pio4: implement .get_multiple and
 .set_multiple

From: Alexandre Belloni
> Implement .get_multiple and .set_multiple to allow reading or setting
> multiple pins simultaneously. Pins in the same bank will all be switched at
> the same time, improving synchronization and performances.

Actually it won't 'improve synchronisation', instead it will lead to
random synchronisation errors and potential metastability if one
pin is used as a clock and another as data, or if the code is reading
a free-flowing counter.

It will improve performance though.

	David

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