linux-kernel - Re: [PATCH v2 4/6] clk: qcom: Use HW_CTRL_TRIGGER flag to switch video GDSC to HW mode

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Message-ID: <5d4ba948-46e2-4b95-95a2-17775f4c9881@linaro.org>
Date:   Thu, 7 Sep 2023 09:36:36 +0200
From:   Konrad Dybcio <konrad.dybcio@...aro.org>
To:     Jagadeesh Kona <quic_jkona@...cinc.com>,
        Abel Vesa <abel.vesa@...aro.org>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Mike Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Taniya Das <tdas@....qualcomm.com>, linux-pm@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm@...r.kernel.org,
        Ajit Pandey <quic_ajipan@...cinc.com>,
        Imran Shaik <quic_imrashai@...cinc.com>
Subject: Re: [PATCH v2 4/6] clk: qcom: Use HW_CTRL_TRIGGER flag to switch
 video GDSC to HW mode

On 7.09.2023 07:55, Jagadeesh Kona wrote:
> 
> 
> On 9/4/2023 9:32 PM, Konrad Dybcio wrote:
>> On 4.09.2023 11:27, Jagadeesh Kona wrote:
>>>
>>>
>>> On 9/2/2023 5:33 PM, Konrad Dybcio wrote:
>>>> On 28.08.2023 08:48, Jagadeesh Kona wrote:
>>>>>
>>>>>
>>>>> On 8/26/2023 4:17 PM, Konrad Dybcio wrote:
>>>>>> On 23.08.2023 12:41, Abel Vesa wrote:
>>>>>>> On 23-08-16 19:56:46, Konrad Dybcio wrote:
>>>>>>>> On 16.08.2023 16:57, Abel Vesa wrote:
>>>>>>>>> From: Jagadeesh Kona <quic_jkona@...cinc.com>
>>>>>>>>>
>>>>>>>>> The current HW_CTRL flag switches the video GDSC to HW control mode as
>>>>>>>>> part of GDSC enable itself, instead of that use HW_CTRL_TRIGGER flag to
>>>>>>>>> give consumer drivers more control and switch the GDSC mode as and when
>>>>>>>>> required.
>>>>>>>>>
>>>>>>>>> HW_CTRL_TRIGGER flag allows consumer drivers to switch the video GDSC to
>>>>>>>>> HW/SW control modes at runtime using dev_pm_genpd_set_hwmode API.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Jagadeesh Kona <quic_jkona@...cinc.com>
>>>>>>>>> Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
>>>>>>>>> ---
>>>>>>>> Do we have any use for the HW_CTRL flag?
>>>>>>>>
>>>>>>>> Perhaps it should be renamed to HW_CTRL_ALWAYS?
>>>>>>>>
>>>>>>>> Or even better, *if and only if* that is necessary, add a common
>>>>>>>> property like "always_hw_managed" to the genpd code?
>>>>>>>
>>>>>>> The HW_CTRL flag is still needed for the consumers that expect the GDSC
>>>>>>> to be have the HW control bit set right after it gets enabled.
>>>>>> Guess the correct question here would be.. Are there any?
>>>>>>
>>>>>
>>>>> Yes, Display GDSC(mdss_gdsc) is required to be controlled always in HW control mode when it is enabled.
>>>> Oh really?
>>>>
>>>> Looking at msm-5.10 techpack, only the SDE RSC driver seems to
>>>> trigger regulator fast mode (so, enabling gdsc hw_ctrl on downstream).
>>>>
>>>
>>> Yes, on downstream, display GDSC has only one consumer(SDE RSC driver) and there are no other consumers. SDE RSC driver switches the GDSC to hw control mode once GDSC is enabled and leaves it in hw control mode. Thanks!
>> Sorry for pulling your tongue here a bit, but would it only concern
>> RPMh SoCs? Designs like SM6115 don't implement RSCs, should they not
>> have HW_CTRL enabled at all times?
>>
> 
> Yes, for RPMh SoCs which have display RSC block, GDSC is switched to HW control mode. For SoCs which doesn't have display RSC block, display driver controls the GDSC in SW mode on downstream. Thanks!
Thanks for explaining!

One last question, I promise.. Should we switch the MDSS GDSC to
HW_CTRL mode only after we start controlling the DISP RSC from Linux,
or should it be done regardless (because of the RPMh solving algos)?

Konrad