linux-kernel - Re: [PATCH v3 1/3] clk: qcom: gdsc: Fix the handling of PWRSTS

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Date:   Mon, 23 Jan 2023 10:00:55 +0530
From:   Rajendra Nayak <quic_rjendra@...cinc.com>
To:     Luca Weiss <luca@...tu.xyz>, <agross@...nel.org>,
        <andersson@...nel.org>, <konrad.dybcio@...ainline.org>,
        <mturquette@...libre.com>, <sboyd@...nel.org>, <mka@...omium.org>
CC:     <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <johan+linaro@...nel.org>, <quic_kriskura@...cinc.com>,
        <dianders@...omium.org>, <linux-clk@...r.kernel.org>,
        <angelogioacchino.delregno@...labora.com>,
        <~postmarketos/upstreaming@...ts.sr.ht>
Subject: Re: [PATCH v3 1/3] clk: qcom: gdsc: Fix the handling of PWRSTS_RET
 support


On 1/22/2023 5:45 AM, Luca Weiss wrote:
> Hi Rajendra,
> 
> On Dienstag, 20. September 2022 13:15:15 CET Rajendra Nayak wrote:
>> GDSCs cannot be transitioned into a Retention state in SW.
>> When either the RETAIN_MEM bit, or both the RETAIN_MEM and
>> RETAIN_PERIPH bits are set, and the GDSC is left ON, the HW
>> takes care of retaining the memory/logic for the domain when
>> the parent domain transitions to power collapse/power off state.
>>
>> On some platforms where the parent domains lowest power state
>> itself is Retention, just leaving the GDSC in ON (without any
>> RETAIN_MEM/RETAIN_PERIPH bits being set) will also transition
>> it to Retention.
>>
>> The existing logic handling the PWRSTS_RET seems to set the
>> RETAIN_MEM/RETAIN_PERIPH bits if the cxcs offsets are specified
>> but then explicitly turns the GDSC OFF as part of _gdsc_disable().
>> Fix that by leaving the GDSC in ON state.
>>
>> Signed-off-by: Rajendra Nayak <quic_rjendra@...cinc.com>
>> Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> ---
>> v3:
>> Updated changelog
>>
>> There are a few existing users of PWRSTS_RET and I am not
>> sure if they would be impacted with this change
>>
>> 1. mdss_gdsc in mmcc-msm8974.c, I am expecting that the
>> gdsc is actually transitioning to OFF and might be left
>> ON as part of this change, atleast till we hit system wide
>> low power state.
>> If we really leak more power because of this
>> change, the right thing to do would be to update .pwrsts for
>> mdss_gdsc to PWRSTS_OFF_ON instead of PWRSTS_RET_ON
>> I dont have a msm8974 hardware, so if anyone who has can report
>> any issues I can take a look further on how to fix it.
> 
> Unfortunately indeed this patch makes problems on msm8974, at least on
> fairphone-fp2 hardware.
> 
> With this patch in place, the screen doesn't initialize correctly in maybe 80%
> of boots and is stuck in weird states, mostly just becomes completely blue.
> 
> Kernel log at least sometimes includes messages like this:
> [   25.847541] dsi_cmds2buf_tx: cmd dma tx failed, type=0x39, data0=0x51,
> len=8, ret=-110
> 
> Do you have anything I can try on msm8974? For now, reverting this patch makes
> display work again on v6.1

hmm, I was really expecting this to leak more power than break anything functionally,
Did you try moving to PWRSTS_OFF_ON instead of PWRSTS_RET_ON for mdss_gdsc?

> 
> Regards
> Luca
> 
>>
>> 2. gpu_gx_gdsc in gpucc-msm8998.c and
>>     gpu_gx_gdsc in gpucc-sdm660.c
>> Both of these seem to add support for 3 power state
>> OFF, RET and ON, however I dont see any logic in gdsc
>> driver to handle 3 different power states.
>> So I am expecting that these are infact just transitioning
>> between ON and OFF and RET state is never really used.
>> The ideal fix for them would be to just update their resp.
>> .pwrsts to PWRSTS_OFF_ON only.
>>
>>   drivers/clk/qcom/gdsc.c | 10 ++++++++++
>>   drivers/clk/qcom/gdsc.h |  5 +++++
>>   2 files changed, 15 insertions(+)
>>
>> diff --git a/drivers/clk/qcom/gdsc.c b/drivers/clk/qcom/gdsc.c
>> index d3244006c661..ccf63771e852 100644
>> --- a/drivers/clk/qcom/gdsc.c
>> +++ b/drivers/clk/qcom/gdsc.c
>> @@ -368,6 +368,16 @@ static int _gdsc_disable(struct gdsc *sc)
>>   	if (sc->pwrsts & PWRSTS_OFF)
>>   		gdsc_clear_mem_on(sc);
>>
>> +	/*
>> +	 * If the GDSC supports only a Retention state, apart from ON,
>> +	 * leave it in ON state.
>> +	 * There is no SW control to transition the GDSC into
>> +	 * Retention state. This happens in HW when the parent
>> +	 * domain goes down to a Low power state
>> +	 */
>> +	if (sc->pwrsts == PWRSTS_RET_ON)
>> +		return 0;
>> +
>>   	ret = gdsc_toggle_logic(sc, GDSC_OFF);
>>   	if (ret)
>>   		return ret;
>> diff --git a/drivers/clk/qcom/gdsc.h b/drivers/clk/qcom/gdsc.h
>> index 5de48c9439b2..981a12c8502d 100644
>> --- a/drivers/clk/qcom/gdsc.h
>> +++ b/drivers/clk/qcom/gdsc.h
>> @@ -49,6 +49,11 @@ struct gdsc {
>>   	const u8			pwrsts;
>>   /* Powerdomain allowable state bitfields */
>>   #define PWRSTS_OFF		BIT(0)
>> +/*
>> + * There is no SW control to transition a GDSC into
>> + * PWRSTS_RET. This happens in HW when the parent
>> + * domain goes down to a low power state
>> + */
>>   #define PWRSTS_RET		BIT(1)
>>   #define PWRSTS_ON		BIT(2)
>>   #define PWRSTS_OFF_ON		(PWRSTS_OFF | PWRSTS_ON)
> 
> 
> 
>