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

[Doug Anderson <dianders@chromium.org>]

Hi,

On Sun, Feb 9, 2020 at 8:01 PM Taniya Das <tdas@codeaurora.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@codeaurora.org>
> Reviewed-by: Douglas Anderson <dianders@chromium.org>

For future reference, if you have someone's tag in your commit message
it's nice to CC them on the email.


> ---
>  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


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