linux-kernel - Re: [PATCH 00/13] Ingenic JZ4740 / JZ4780 pinctrl driver

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Date:   Fri, 20 Jan 2017 11:17:28 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Maarten ter Huurne <maarten@...ewalker.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Paul Burton <paul.burton@...tec.com>,
        linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linux MIPS <linux-mips@...ux-mips.org>,
        linux-mmc@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-pwm@...r.kernel.org, linux-fbdev@...r.kernel.org,
        James Hogan <james.hogan@...tec.com>
Subject: Re: [PATCH 00/13] Ingenic JZ4740 / JZ4780 pinctrl driver

Le 2017-01-20 09:40, Linus Walleij a écrit :

> On Thu, Jan 19, 2017 at 12:19 PM, Paul Cercueil <paul@...pouillou.net> 
> wrote:
> 
>> The problem with pinctrl and PWM, is that the pinctrl API works by 
>> "states". A default state, sleep state, and basically any custom state 
>> that the devicetree provides. This works well until you need to 
>> control individually each pin; with 8 pins, you would need 2^8 states, 
>> each one corresponding to a given configuration.
> 
> I do not really understand, do you really use all 2^8 states in a given
> system?
> 
> The pin control states are to be used for practical situations, not
> for all theoretical situations.
> 
> You should define in your device tree the states that your
> particular system will use. Not all possible states on all possible
> systems.
> 

Well, that was if I wanted to dynamically set/unset the pin mux and
configuration when requesting/freeing a PWM. Then I'd need 2^x states
for X PWM pins.

Anyway, a static configuration works for me too. If at some point I
want dynamic configuration of the pins then I'll make the PWM driver
handle only one PWM pin and create one driver instance for each pin.

Regards,
-Paul