linux-kernel - Re: [PATCH v2 2/4] soc: qcom: rpmh: Add support to read back resource settings

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Message-ID: <9a227c15-dc60-4086-8d81-f80e3398a083@oss.qualcomm.com>
Date: Thu, 23 Oct 2025 15:16:09 +0530
From: "Maulik Shah (mkshah)" <maulik.shah@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Kamal Wadhwa <kamal.wadhwa@....qualcomm.com>
Cc: Konrad Dybcio <konradybcio@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] soc: qcom: rpmh: Add support to read back resource
 settings



On 10/23/2025 2:39 PM, Konrad Dybcio wrote:
> On 10/23/25 10:57 AM, Maulik Shah (mkshah) wrote:
>>
>>
>> On 10/23/2025 1:47 PM, Konrad Dybcio wrote:
>>> On 10/23/25 6:46 AM, Maulik Shah (mkshah) wrote:
>>>>
>>>>
>>>> On 10/23/2025 2:51 AM, Bjorn Andersson wrote:
>>>>> On Wed, Oct 22, 2025 at 02:38:54AM +0530, Kamal Wadhwa wrote:
>>>>>> From: Maulik Shah <maulik.shah@....qualcomm.com>
>>>>>>
>>>>>> All rpmh_*() APIs so far have supported placing votes for various
>>>>>> resource settings but the H/W also have option to read resource
>>>>>> settings.
>>>>>>
>>>>>> This change adds a new rpmh_read() API to allow clients
>>>>>> to read back resource setting from H/W. This will be useful for
>>>>>> clients like regulators, which currently don't have a way to know
>>>>>> the settings applied during bootloader stage.
>>>>>>
>>>>>
>>>>> Allow me to express my disappointment over the fact that you sat on this
>>>>> for 7 years!
>>>>
>>>> This was a dead API (even in downstream) with no user since SDM845/ 7 years.
>>>> Read support was eventually removed from downstream driver too for the same reason.
>>>> There were early discussions to remove read support from RSC H/W, due to lack of users.
>>>> Its not realized yet and all SoCs still supports read.
>>>
>>> Can we read BCM states from HLOS this way too?
>>
>> Yes, Any of ARC/BCM/VRM can be read to get HLOS/DRV2 votes.
> 
> Wow this is amazing..
> 
> Do you have code for this already, or should I hack on it?

No, it won't be of much help, as i said above it gets HLOS/DRV2 votes only for a given resource.
More specifically, the read does not give the aggregated vote result across all the DRVs.

Thanks,
Maulik

> 
> Konrad