linux-kernel - Re: [PATCH] soc: qcom: icc-bwmon: Don't ignore return values of regmap functions

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Date:   Tue, 20 Jun 2023 20:59:48 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] soc: qcom: icc-bwmon: Don't ignore return values of
 regmap functions

On 20.06.2023 20:15, Krzysztof Kozlowski wrote:
> On 20/06/2023 20:14, Bjorn Andersson wrote:
>> On Thu, Jun 15, 2023 at 11:26:13PM +0200, Krzysztof Kozlowski wrote:
>>> On 15/06/2023 23:12, Konrad Dybcio wrote:
>>>> As it turns out, not all regmap accesses succeed. Not knowing this is
>>>> particularly suboptimal when there's a breaking change to the regmap
>>>> APIs. Monitor the return values of regmap_ calls and propagate errors,
>>>> should any occur.
>>>>
>>>> To keep any level of readability in bwmon_enable(), add some comments
>>>> to separate the logical blocks.
>>>>
>>>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
>>>
>>> Nice coincidence, I just had some talks with a friend about uselessness
>>> (IMHO) of regmap MMIO return status checks.
>>>
>>> Sorry, for me most of this makes the code difficult to read for no gain.
>>> Errors are not real. This is some artificial problem. Solving it makes
>>> code less maintainable.
>>>
>>> If we used here readl/writel, you would not add any checks, right? Then
>>> don't add for regmap mmio.
>>>
>>
>> I agree, the mmio regmap interface should only fail because of bugs or
>> things are misconfigured. Would be nice to capture that in a WARN_ON()
>> or something...
>>
> 
> One choice could be to have for entire functions doing reads/writes:
> 
> 	ret = 0;
> 	ret != regmap_write();
> 	ret != regmap_write();
> 	ret != regmap_write();
> 	return ret;
> 
> and handle this in the caller somehow. I don't think that aborting such
> chain early, just because regmap mmio failures, makes sense.
Meh, perhaps let's just forget about this patch.

Konrad
> 
> Best regards,
> Krzysztof
>