linux-kernel - Re: [PATCH RFC 1/3] drm/msm/adreno: Add support for ACD

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Message-ID: <e1871824-78c8-436f-a41c-16ac1614004a@oss.qualcomm.com>
Date: Mon, 4 Nov 2024 15:18:03 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Akhil P Oommen <quic_akhilpo@...cinc.com>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH RFC 1/3] drm/msm/adreno: Add support for ACD

On 22.10.2024 12:09 AM, Akhil P Oommen wrote:
> On Mon, Oct 21, 2024 at 11:38:41AM +0200, Konrad Dybcio wrote:
>> On 11.10.2024 10:29 PM, Akhil P Oommen wrote:
>>> ACD a.k.a Adaptive Clock Distribution is a feature which helps to reduce
>>> the power consumption. In some chipsets, it is also a requirement to
>>> support higher GPU frequencies. This patch adds support for GPU ACD by
>>> sending necessary data to GMU and AOSS. The feature support for the
>>> chipset is detected based on devicetree data.
>>>
>>> Signed-off-by: Akhil P Oommen <quic_akhilpo@...cinc.com>
>>> ---
>>
>> [...]
>>
>>> +
>>> +	/* Initialize qmp node to talk to AOSS */
>>> +	gmu->qmp = qmp_get(gmu->dev);
>>> +	if (IS_ERR(gmu->qmp)) {
>>> +		cmd->enable_by_level = 0;
>>> +		return dev_err_probe(gmu->dev, PTR_ERR(gmu->qmp), "Failed to initialize qmp\n");
>>> +	}
>>
>> I'm still in favor of keeping qmp_get where it currently is, so that
>> probe can fail/defer faster
> 
> Sorry, I somehow missed this email from you until now.
> 
> If it fails, then it probably doesn't matter if it is a bit late. But for defer, isn't there
> some optimizations to track the dependency from devicetree data? I am
> not entirely sure!

There's devlink for clocks/supplies etc, it doesn't apply universally
for all phandle references IIUC.

> 
> Since qmp node is related to ACD, I felt it is better to:
>   1. Keep all acd probe related code in a single place.
>   2. Be more opportunistic in skipping qmp_get() wherever possible.
> 
> But if you still have strong opinion on this, I can move it back in the
> next revision (v3).

I suppose the answer is yes, I have a strong opinion :D

Konrad