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

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Message-ID: <8580c092-3e1f-4b53-8330-ac1746b7a126@oss.qualcomm.com>
Date: Mon, 17 Nov 2025 13:34:26 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: "Maulik Shah (mkshah)" <maulik.shah@....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 11/17/25 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?

Konrad