linux-kernel - Re: [RESEND PATCHv4 1/1] drivers/amba: add reset control to amba bus probe

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Date:   Fri, 23 Aug 2019 11:19:42 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Dinh Nguyen <dinguyen@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Rob Herring <robh@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Frank Rowand <frowand.list@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RESEND PATCHv4 1/1] drivers/amba: add reset control to amba bus probe

On Tue, Aug 20, 2019 at 4:58 PM Dinh Nguyen <dinguyen@...nel.org> wrote:

> @@ -401,6 +402,26 @@ static int amba_device_try_add(struct amba_device *dev, struct resource *parent)
>         ret = amba_get_enable_pclk(dev);
>         if (ret == 0) {
>                 u32 pid, cid;
> +               int count;
> +               struct reset_control *rstc;
> +
> +               /*
> +                * Find reset control(s) of the amba bus and de-assert them.
> +                */
> +               count = reset_control_get_count(&dev->dev);
> +               while (count > 0) {
> +                       rstc = of_reset_control_get_shared_by_index(dev->dev.of_node, count - 1);
> +                       if (IS_ERR(rstc)) {
> +                               if (PTR_ERR(rstc) == -EPROBE_DEFER)
> +                                       ret = -EPROBE_DEFER;
> +                               else
> +                                       dev_err(&dev->dev, "Can't get amba reset!\n");
> +                               break;
> +                       }
> +                       reset_control_deassert(rstc);
> +                       reset_control_put(rstc);
> +                       count--;
> +               }

I'm not normally a footprint person, but the looks of the stubs in
<linux/reset.h> makes me suspicious whether this will have zero impact
in size on platforms without reset controllers.

Can you just ls -al on the kernel without CONFIG_RESET_CONTROLLER
before and after this patch and ascertain that it has zero footprint effect?

If it doesn't I'd sure like to break this into its own function and
stick a if (!IS_ENABLED(CONFIG_RESET_CONTROLLER)) return 0;
in there to make sure the compiler drops it.

Also it'd be nice to get Philipp's ACK on the semantics, though they
look correct to me.

Yours,
Linus Walleij