linux-kernel - Re: [PATCH V4 5/5] gpio: gpio-xilinx: Add check if width exceeds 32

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Date:   Thu, 7 Jan 2021 11:47:40 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Michal Simek <michal.simek@...inx.com>
Cc:     Srinivas Neeli <srinivas.neeli@...inx.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Shubhrajyoti Datta <shubhrajyoti.datta@...inx.com>,
        sgoud@...inx.com, Robert Hancock <hancock@...systems.ca>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        Syed Nayyar Waris <syednwaris@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        git@...inx.com
Subject: Re: [PATCH V4 5/5] gpio: gpio-xilinx: Add check if width exceeds 32

On Thu, Jan 7, 2021 at 11:29 AM Michal Simek <michal.simek@...inx.com> wrote:
> On 07. 01. 21 11:17, Linus Walleij wrote:
> > On Wed, Jan 6, 2021 at 1:27 PM Srinivas Neeli <srinivas.neeli@...inx.com> wrote:

> >> @@ -591,6 +591,9 @@ static int xgpio_probe(struct platform_device *pdev)
> >>         if (of_property_read_u32(np, "xlnx,gpio-width", &chip->gpio_width[0]))
> >>                 chip->gpio_width[0] = 32;
> >
> > This xlnx,gpio-width seems very much like the standard ngpios property
> > from Documentation/devicetree/bindings/gpio/gpio.txt
> > but I guess not much to do about that now. :/
> >
> > Do you think you can add support for both?
>
> support for both is definitely possible but we need to handle also gpio
> width for second channel referenced by xlnx,gpio2-widht now.
>
> It means we could end up in situation which can be misleading for users
> where ngpios will be 10 and xlnx,gpio2-width another 10 and in total we
> have 20 gpios.

OK that is confusing. Let's not do that then.

> I think that it is better not to start to mess with ngpios property not
> to confuse people which are coming from other SOCs because ngpios can
> suggest all gpios assigned to this controller.

OK I agree.

> >> +       if (chip->gpio_width[0] > 32)
> >> +               return -EINVAL;
> >
> > This looks OK.
>
> Does it mean ack for this patch?

Yeah after explanations this patch is fine:
Acked-by: Linus Walleij <linus.walleij@...aro.org>

It's just that this hardware with paired controllers is a bit weird so it will
lead to discussions all the time because it's hard to understand.

Yours,
Linus Walleij