linux-kernel - Re: [PATCH v2 2/2] clk: qcom: gpucc: Add support for GX GDSC for SC7180

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Date:   Tue, 11 Feb 2020 08:20:53 +0530
From:   Taniya Das <tdas@...eaurora.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Stephen Boyd <sboyd@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh@...nel.org>,
        David Brown <david.brown@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:ARM/QUALCOMM SUPPORT" <linux-soc@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Gross <agross@...nel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH v2 2/2] clk: qcom: gpucc: Add support for GX GDSC for
 SC7180

Hi Doug,

On 2/10/2020 11:19 PM, Doug Anderson wrote:
> Hi,
> 
> On Sun, Feb 9, 2020 at 8:01 PM Taniya Das <tdas@...eaurora.org> wrote:
>>
>> Most of the time the CPU should not be touching the GX domain on the
>> GPU except for a very special use case when the CPU needs to force the
>> GX headswitch off. Add the GX domain for that use case.  As part of
>> this add a dummy enable function for the GX gdsc to simulate success
>> so that the pm_runtime reference counting is correct.  This matches
>> what was done in sdm845 in commit 85a3d920d30a ("clk: qcom: Add a
>> dummy enable function for GX gdsc").
>>
>> Signed-off-by: Taniya Das <tdas@...eaurora.org>
>> Reviewed-by: Douglas Anderson <dianders@...omium.org>
> 
> For future reference, if you have someone's tag in your commit message
> it's nice to CC them on the email.
> 
> 

My bad my miss.

>> ---
>>   drivers/clk/qcom/gpucc-sc7180.c | 37 +++++++++++++++++++++++++++++++++++++
>>   1 file changed, 37 insertions(+)
>>
>> diff --git a/drivers/clk/qcom/gpucc-sc7180.c b/drivers/clk/qcom/gpucc-sc7180.c
>> index a96c0b9..7b656b6 100644
>> --- a/drivers/clk/qcom/gpucc-sc7180.c
>> +++ b/drivers/clk/qcom/gpucc-sc7180.c
>> @@ -170,8 +170,45 @@ static struct gdsc cx_gdsc = {
>>          .flags = VOTABLE,
>>   };
>>
>> +/*
>> + * On SC7180 the GPU GX domain is *almost* entirely controlled by the GMU
>> + * running in the CX domain so the CPU doesn't need to know anything about the
>> + * GX domain EXCEPT....
>> + *
>> + * Hardware constraints dictate that the GX be powered down before the CX. If
>> + * the GMU crashes it could leave the GX on. In order to successfully bring back
>> + * the device the CPU needs to disable the GX headswitch. There being no sane
>> + * way to reach in and touch that register from deep inside the GPU driver we
>> + * need to set up the infrastructure to be able to ensure that the GPU can
>> + * ensure that the GX is off during this super special case. We do this by
>> + * defining a GX gdsc with a dummy enable function and a "default" disable
>> + * function.
>> + *
>> + * This allows us to attach with genpd_dev_pm_attach_by_name() in the GPU
>> + * driver. During power up, nothing will happen from the CPU (and the GMU will
>> + * power up normally but during power down this will ensure that the GX domain
>> + * is *really* off - this gives us a semi standard way of doing what we need.
>> + */
>> +static int gx_gdsc_enable(struct generic_pm_domain *domain)
>> +{
>> +       /* Do nothing but give genpd the impression that we were successful */
>> +       return 0;
>> +}
>> +
>> +static struct gdsc gx_gdsc = {
>> +       .gdscr = 0x100c,
>> +       .clamp_io_ctrl = 0x1508,
>> +       .pd = {
>> +               .name = "gx_gdsc",
>> +               .power_on = gx_gdsc_enable,
>> +       },
>> +       .pwrsts = PWRSTS_OFF_ON,
>> +       .flags = CLAMP_IO,
> 
> In my previous reply [1], I asked about these flags and if it was
> intentional that they were different from sdm845.  I did see a private
> response, but no public one.  In the future note that it's good to
> reply publicly so everyone understands what happened.  In this case, I
> was told "the GDSC's on 845 and SC7180 are different and hence the
> change in flags is expected".  That answers my question and thus I'm
> fine with my tag being here.  It also looks like you took my other
> review feedback on v1, which is nice.
> 
> 
> -Doug
> 

I am unable to respond to the other thread, thus we put out the reply.

> 
> [1] https://lore.kernel.org/r/CAD=FV=V6yM7UJwu0ZLPCqmDgV9FS4=g+wcLg0TV51b72zvWT9Q@mail.gmail.com
> 

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