linux-kernel - Re: [PATCH 2/3] pinctrl: msm: Mux out gpio function with gpio

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Message-ID: <CAD=FV=VpFR4hpREnWpvG2MQAONheKtNfLkyNM8-AFXMcGD7OPQ@mail.gmail.com>
Date:   Mon, 18 Jun 2018 16:54:49 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-gpio@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Subject: Re: [PATCH 2/3] pinctrl: msm: Mux out gpio function with gpio_request()

Hi,

On Mon, Jun 18, 2018 at 1:52 PM, Stephen Boyd <swboyd@...omium.org> wrote:
> We rely on devices to use pinmuxing configurations in DT to select the
> GPIO function (function 0) if they're going to use the gpio in GPIO
> mode. Let's simplify things for driver authors by implementing
> gpio_request_enable() for this pinctrl driver to mux out the GPIO
> function when the gpio is use from gpiolib.
>
> Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
> Cc: Doug Anderson <dianders@...omium.org>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---
>  drivers/pinctrl/qcom/pinctrl-msm.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/drivers/pinctrl/qcom/pinctrl-msm.c b/drivers/pinctrl/qcom/pinctrl-msm.c
> index 3563c4394837..eacfc5b85f7f 100644
> --- a/drivers/pinctrl/qcom/pinctrl-msm.c
> +++ b/drivers/pinctrl/qcom/pinctrl-msm.c
> @@ -176,11 +176,27 @@ static int msm_pinmux_set_mux(struct pinctrl_dev *pctldev,
>         return 0;
>  }
>
> +static int msm_pinmux_request_gpio(struct pinctrl_dev *pctldev,
> +                                  struct pinctrl_gpio_range *range,
> +                                  unsigned offset)
> +{
> +       struct msm_pinctrl *pctrl = pinctrl_dev_get_drvdata(pctldev);
> +       const struct msm_pingroup *g = &pctrl->soc->groups[offset];
> +
> +       /* No funcs? Probably ACPI so can't do anything here */
> +       if (!g->nfuncs)
> +               return 0;

Is there a reason why you'd want to return 0 instead of some sort of
error code?  Wouldn't you want to know that this pin can't be a GPIO?
Another non-ACPI example is sdc2 on sdm845 and it seems like you'd
want to know if someone tried to set one of those as a GPIO.

...oh, but I guess ufs_reset also has no funcs but it still probably
wants to use the GPIO framework to write something.  Hrmmm...  Maybe
check if either in_bit or out_bit is not -1?


> +
> +       /* For now assume function 0 is GPIO because it always is */
> +       return msm_pinmux_set_mux(pctldev, 0, offset);

nit: should you be consistent with msm_pinmux_set_mux() and call it
"group" instead of "offset"?  It looks like it's supposed to be the
same thing...


-Doug