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 10:42:49 -0500
From:   Dinh Nguyen <dinguyen@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.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 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);
>> +               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?

Thanks for the review. I checked it, and indeed, it does have a 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.
> 

Dinh