[Nouveau] [RFC PATCH v2] clk: Remove BYPASS_PLL_CHECK from PLLs

[Ilia Mirkin]

Can you check to see if that bit was set prior to entering the code? I
wonder if you can just restore it if it was there, and leave it if
it's not?

On Wed, Sep 4, 2019 at 10:28 AM Mark Menzynski <mmenzyns at redhat.com> wrote:
>
> I have looked at problem with Fermi GPUs where changing to higher clock
> led to really bad perfomance (with GpuTest 20x worse perfomance) and later also crashes of the nouveau. It seemed
> to be affected by Shader Clock in Voltage Entries in the video BIOS. Disabling
> BYPASS_PLL_CHECK in CLK0_CTRL seems to completely fix the issue. I have
> tried to search this BYPASS_PLL_CHECK in Nvidia traces but seemed it
> wasn't used nowhere for CLK settings.
>
> Removing this works fine, but I don't know what it's really for.
> Actual bit setting this BYPASS_PLL_CHECK is on 0x10:
>         lookup -ac0 0x137000 0x10
>         PCLOCK.CLK0_CTRL => { BYPASS_PLL_CHECK | UNK12 = 0 }
> Also, disabling this bit on other CLKs doesn't seem to break anything.
>
> v2: Add back PLL lock test
>
> Signed-off-by: Mark Menzynski <mmenzyns at redhat.com>
> ---
>  drm/nouveau/nvkm/subdev/clk/gf100.c | 1 -
>  drm/nouveau/nvkm/subdev/clk/gk104.c | 1 -
>  2 files changed, 2 deletions(-)
>
> diff --git a/drm/nouveau/nvkm/subdev/clk/gf100.c b/drm/nouveau/nvkm/subdev/clk/gf100.c
> index 7f67f9f5..fe56817b 100644
> --- a/drm/nouveau/nvkm/subdev/clk/gf100.c
> +++ b/drm/nouveau/nvkm/subdev/clk/gf100.c
> @@ -381,7 +381,6 @@ gf100_clk_prog_2(struct gf100_clk *clk, int idx)
>                                 if (nvkm_rd32(device, addr + 0x00) & 0x00020000)
>                                         break;
>                         );
> -                       nvkm_mask(device, addr + 0x00, 0x00000010, 0x00000010);
>
>                         /* Enable sync mode */
>                         nvkm_mask(device, addr + 0x00, 0x00000004, 0x00000004);
> diff --git a/drm/nouveau/nvkm/subdev/clk/gk104.c b/drm/nouveau/nvkm/subdev/clk/gk104.c
> index 0b37e3da..22cac304 100644
> --- a/drm/nouveau/nvkm/subdev/clk/gk104.c
> +++ b/drm/nouveau/nvkm/subdev/clk/gk104.c
> @@ -400,7 +400,6 @@ gk104_clk_prog_2(struct gk104_clk *clk, int idx)
>                         if (nvkm_rd32(device, addr + 0x00) & 0x00020000)
>                                 break;
>                 );
> -               nvkm_mask(device, addr + 0x00, 0x00000010, 0x00000010);
>
>                 /* Enable sync mode */
>                 nvkm_mask(device, addr + 0x00, 0x00000004, 0x00000004);
> --
> 2.21.0
>
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