linux-kernel - Re: [PATCH 10/20] gpio: pca953x: Add optional reset gpio control

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Date:   Fri, 30 Dec 2016 10:03:53 -0800
From:   Steve Longerbeam <slongerbeam@...il.com>
To:     Linus Walleij <linus.walleij@...aro.org>, LW@...O-electronics.de
Cc:     Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Alexandre Courbot <gnurou@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>
Subject: Re: [PATCH 10/20] gpio: pca953x: Add optional reset gpio control

Hi Linus, Lothar,


On 12/30/2016 05:17 AM, Linus Walleij wrote:
> On Thu, Dec 29, 2016 at 11:27 PM, Steve Longerbeam
> <slongerbeam@...il.com> wrote:
>
>> Add optional reset-gpios pin control. If present, de-assert the
>> specified reset gpio pin to bring the chip out of reset.
>>
>> Signed-off-by: Steve Longerbeam <steve_longerbeam@...tor.com>
>> Cc: Linus Walleij <linus.walleij@...aro.org>
>> Cc: Alexandre Courbot <gnurou@...il.com>
>> Cc: linux-gpio@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org
> This seems like a separate patch from the other 19 patches so please send it
> separately so I can handle logistics easier in the future.

Ok, I'll send the next version separately.

>
>
>> @@ -133,6 +134,7 @@ struct pca953x_chip {
>>          const char *const *names;
>>          unsigned long driver_data;
>>          struct regulator *regulator;
>> +       struct gpio_desc *reset_gpio;
> Why do you even keep this around in the device state container?
>
> As you only use it in the probe() function, use a local variable.
>
> The descriptor will be free():ed by the devm infrastructure anyways.

I think my reasoning for putting the gpio handle into the device
struct was for possibly using it for run-time reset control at some
point. But that could be done later if needed, so I'll go ahead and
make it local.

>> +               /* see if we need to de-assert a reset pin */
>> +               chip->reset_gpio = devm_gpiod_get_optional(&client->dev,
>> +                                                          "reset",
>> +                                                          GPIOD_OUT_LOW);
>> +               if (IS_ERR(chip->reset_gpio)) {
>> +                       dev_err(&client->dev, "request for reset pin failed\n");
>> +                       return PTR_ERR(chip->reset_gpio);
>> +               }
> Nice.
>
>> +               if (chip->reset_gpio) {
>> +                       /* bring chip out of reset */
>> +                       dev_info(&client->dev, "releasing reset\n");
>> +                       gpiod_set_value(chip->reset_gpio, 0);
>> +               }
> Is this really needed given that you set it low in the
> devm_gpiod_get_optional()?

Yep, this is left over from a previous iteration, but it isn't needed now.
I'll remove it.

Steve