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

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Date:   Mon, 26 Aug 2019 10:27:14 -0500
From:   Dinh Nguyen <dinguyen@...nel.org>
To:     Philipp Zabel <p.zabel@...gutronix.de>,
        Linus Walleij <linus.walleij@...aro.org>
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

Hi Philipp,

On 8/26/19 3:57 AM, Philipp Zabel wrote:
> Hi Dinh, Linus,
> 
> On Fri, 2019-08-23 at 10:42 -0500, Dinh Nguyen wrote:
>>
>> On 8/23/19 4:19 AM, Linus Walleij wrote:
>>> 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);
> 
> The reset_control_get_count() inline stub returns -ENOENT, so the
> compiler can throw away the complete loop.
> 
>>>> +               while (count > 0) {
>>>> +                       rstc = of_reset_control_get_shared_by_index(dev->dev.of_node, count - 1);
> 
> Since resets are looked up with of_reset_control_get, I'd use
> of_reset_control_get_count() above for consistency. But see below:
> 

reset_control_get_count() ultimately calls of_reset_control_get_count()
and it looks like of_reset_control_get_count() is not exported.

>>>> +                       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--;
>>>> +               }
> 
> It looks like the order of deassertions is irrelevant. If so,
> You can use of_reset_control_array_get() to simplify this:
> 
> +		rstc = of_reset_control_array_get_optional_shared(dev->dev.of_node);
> +		if (IS_ERR(rstc)) {
> +			if (PTR_ERR(rstc) != -EPROBE_DEFER)
> +				dev_err(&dev->dev, "Can't get amba reset!\n");
> +			return PTR_ERR(rstc);
> +		}
> +		reset_control_deassert(rstc);
> +		reset_control_put(rstc);
> 

Thanks for the review! I'll post v5 shortly.

Dinh