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

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Message-ID: <cd7420d3-ceca-4a65-bf19-bed4452d9576@oss.qualcomm.com>
Date: Fri, 21 Nov 2025 14:11:16 +0530
From: "Maulik Shah (mkshah)" <maulik.shah@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Kamal Wadhwa <kamal.wadhwa@....qualcomm.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>
Cc: 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 11/17/2025 6:04 PM, Konrad Dybcio wrote:
> On 11/17/25 9:26 AM, Maulik Shah (mkshah) wrote:
>>
>>
>> On 11/12/2025 4:56 PM, Konrad Dybcio wrote:
>>> On 10/21/25 11:08 PM, 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.
>>>>
>>>> Link: https://lore.kernel.org/r/20250623-add-rpmh-read-support-v1-1-ae583d260195@oss.qualcomm.com
>>>> Signed-off-by: Maulik Shah <maulik.shah@....qualcomm.com>
>>>> Signed-off-by: Kamal Wadhwa <kamal.wadhwa@....qualcomm.com>
>>>> ---
>>>
>>> [...]
>>>
>>>> +int rpmh_read(const struct device *dev, struct tcs_cmd *cmd)
>>>> +{
>>>> +	DECLARE_COMPLETION_ONSTACK(compl);
>>>> +	DEFINE_RPMH_MSG_ONSTACK(dev, RPMH_ACTIVE_ONLY_STATE, &compl, rpm_msg);
>>>> +	int ret;
>>>> +
>>>> +	ret = __fill_rpmh_msg(&rpm_msg, RPMH_ACTIVE_ONLY_STATE, cmd, 1, true);
>>>> +	if (ret)
>>>> +		return ret;
>>>> +
>>>> +	ret = __rpmh_write(dev, RPMH_ACTIVE_ONLY_STATE, &rpm_msg);
>>>
>>> Is there a reason for making this ACTIVE_ONLY?
>>
>> Yes, using ACTIVE_ONLY makes the read request place immediately to read back the current resource setting.
>> Sleep/Wake are H/W based trigger and are not applicable for this API.
> 
> Huh? So if I send a read request with e.g. SLEEP_STATE, it would only
> get fulfilled upon an active->sleep transition?
> 

Read requests will get fulfilled immediately with the return of the current resource setting,
there is no separate active/sleep/wake vote values that can be read, put it other way the
rpmh_read() API do not take any "enum rpmh_state state" argument like various rpmh_write_*() APIs.

Thanks,
Maulik