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

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Message-ID: <7656e8f6-e281-4f7b-9ff4-1b2722234091@linaro.org>
Date: Mon, 27 Oct 2025 15:38:21 +0100
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
 "Maulik Shah (mkshah)" <maulik.shah@....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 10/27/25 14:29, Konrad Dybcio wrote:
> On 10/23/25 11:46 AM, Maulik Shah (mkshah) wrote:
>>
>>
>> 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.
> 
> Hm, perhaps it could still be of *some* use
> 
> But maybe reading back rpmhpd and rpmhcc states would be of more
> use!

The interconnect core definitely supports reading back the state at boot.

Neil

> 
> Konrad