linux-kernel - Re: [PATCH] arm64: dts: qcom: add IPA qcom,qmp property

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Date:   Thu, 3 Feb 2022 05:27:49 -0600
From:   Alex Elder <elder@...aro.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     bjorn.andersson@...aro.org, agross@...nel.org, robh+dt@...nel.org,
        davem@...emloft.net, mka@...omium.org, evgreen@...omium.org,
        cpratapa@...eaurora.org, avuyyuru@...eaurora.org,
        jponduru@...eaurora.org, subashab@...eaurora.org, elder@...nel.org,
        linux-arm-msm@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: qcom: add IPA qcom,qmp property

On 2/2/22 11:06 PM, Jakub Kicinski wrote:
> On Tue,  1 Feb 2022 08:07:23 -0600 Alex Elder wrote:
>> At least three platforms require the "qcom,qmp" property to be
>> specified, so the IPA driver can request register retention across
>> power collapse.  Update DTS files accordingly.
>>
>> Signed-off-by: Alex Elder <elder@...aro.org>
>> ---
>>
>> Dave, Jakub, please let Bjorn take this through the Qualcomm tree.
> 
> I don't know much about DT but the patch defining the property is
> targeting net - will it not cause validation errors? Or Bjorn knows
> to wait for the fixes to propagate? Or it doesn't matter? :)

It might matter sometimes, but in this case it does not.

If the DT property is present but never referenced by the
code, it doesn't matter.

The code in this patch looks up the DT property, and its
behavior is affected by whether the property is there
or not.  If it's not there, it's treated as an error
that can be safely ignored.

In the case this fix is actually needed, we'll need
both the code present and DT property defined.  If
the code is there but not the property, it's OK, but
the bug won't be fixed quite yet.

					-Alex