Date:   Wed, 28 Sep 2022 09:39:58 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Bjorn Andersson <andersson@...nel.org>
Cc:     Rajendra Nayak <quic_rjendra@...cinc.com>, agross@...nel.org,
        konrad.dybcio@...ainline.org, mturquette@...libre.com,
        sboyd@...nel.org, mka@...omium.org, 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
Subject: Re: [PATCH v3 1/3] clk: qcom: gdsc: Fix the handling of PWRSTS_RET
 support

Il 27/09/22 19:05, Bjorn Andersson ha scritto:
> On Tue, Sep 27, 2022 at 01:57:59PM +0200, AngeloGioacchino Del Regno wrote:
>> Il 27/09/22 05:02, Bjorn Andersson ha scritto:
>>> On Tue, Sep 20, 2022 at 02:39:21PM +0200, AngeloGioacchino Del Regno wrote:
>>>> Il 20/09/22 13:15, Rajendra Nayak ha scritto:
>>>>> 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.
>>>>
>>>> I think that the safest option is to add a PWRSTS_RET_HW_CTRL flag (or similar),
>>>> used for the specific cases of SC7180 and SC7280 (and possibly others) where the
>>>> GDSC is automatically transitioned to a Retention state by HW control, with no
>>>> required software (kernel driver) intervention.
>>>>
>>>>>
>>>>> 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.
>>>>
>>>> static int gdsc_init(struct gdsc *sc)
>>>> {
>>>>
>>>> 	...
>>>>
>>>> 	if (on || (sc->pwrsts & PWRSTS_RET))
>>>> 		gdsc_force_mem_on(sc);
>>>> 	else
>>>> 		gdsc_clear_mem_on(sc);
>>>>
>>>> 	...
>>>> }
>>>>
>>>> On MSM8998 and SDM630/636/660, we're reaching that point with a GDSC that is
>>>> left OFF from the bootloader, but we want (at least for 630/660) memretain
>>>> without periph-retain: this is required to make the hypervisor happy.
>>>>
>>>
>>> Forgive me Angelo, but can you please help me understand your concern
>>> here?
>>>
>>> Are yous saying that the valid states for 8998/660 are PWRSTS_OFF_ON,
>>> but you also want gdsc_force_mem_on() - with NO_RET_PERIPH?
>>>
>>>
>>> It seems to me that as Rajendra's patch is written, the gpu_gx_gdsc
>>> won't be affected, because pwrsts != PWRSTS_RET. So this is a question
>>> about the validity of fixing the pwrsts in gpucc-msm8998, rather than
>>> about this patch in itself?
>>>
>>
>> Hello Bjorn,
>>
>> my replies were related to this part of the commit description:
>>
>>>>> The ideal fix for them would be to just update their resp.
>>>>> .pwrsts to PWRSTS_OFF_ON only.
>>
>> By updating MSM8998 and SDM660's gpu_gx_gdsc to remove PWRSTS_RET, the gdsc_init()
>> flow will change, as in the aforementioned branch, `on` will be false, hence,
>> we will clear RETAIN_MEM during the gpu_gx_gdsc initialization, producing side
>> effects.
>> I agree on the fact that PWRSTS_RET was *not* handled correctly before this commit
>> and this alone will not produce any side effects on MSM8998, nor SDM660.
>>
>> So yes, this is a discussion about the validity of fixing the pwrsts in
>> gpucc-msm8998 and in gpucc-sdm660.c.
>>
> 
> Okay, now I understand the context, I will move ahead and merge these
> patches then.
> 
> 
> And for 8998/660 you're saying that the GDSC is found to be OFF at boot
> and in runtime you're going to bounce it between on and off in software,
> but you need RETAIN_MEM set?
> 

Correct.

> If that's the case this GDSC can be in all 3 states. But as you can
> find in the discussions that lead up to this discussion, we don't have a
> way to represent this to the clients (today).
> 

Yes I know and agree.

Regards,
Angelo

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