[PATCH] drm/amdgpu/gfx11: need acquire mutex before access CP_VMID_RESET

[Xiao, Jack]

[AMD Official Use Only - General]

It's already protected by the reset lock. In my understanding, soft reset should not run in parallel.

Regards,
Jack

-----Original Message-----
From: Alex Deucher <alexdeucher at gmail.com>
Sent: Wednesday, December 20, 2023 1:04 AM
To: Xiao, Jack <Jack.Xiao at amd.com>
Cc: amd-gfx at lists.freedesktop.org; Deucher, Alexander <Alexander.Deucher at amd.com>; Zhang, Hawking <Hawking.Zhang at amd.com>
Subject: Re: [PATCH] drm/amdgpu/gfx11: need acquire mutex before access CP_VMID_RESET

On Tue, Dec 19, 2023 at 4:30 AM Jack Xiao <Jack.Xiao at amd.com> wrote:
>
> It's required to take the gfx mutex before access to CP_VMID_RESET,
> for there is a race condition with CP firmware to write the register.
>
> Signed-off-by: Jack Xiao <Jack.Xiao at amd.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/gfx_v11_0.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v11_0.c
> b/drivers/gpu/drm/amd/amdgpu/gfx_v11_0.c
> index bdcf96df69e6..ae3370d34d11 100644
> --- a/drivers/gpu/drm/amd/amdgpu/gfx_v11_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v11_0.c
> @@ -4518,6 +4518,22 @@ static int gfx_v11_0_soft_reset(void *handle)
>                 }
>         }
>

We probably want a CPU mutex or spinlock to protect this as well unless this is already protected by the reset lock.

Alex

> +       /* Try to require the gfx mutex before access to CP_VMID_RESET */
> +       for (i = 0; i < adev->usec_timeout; i++) {
> +               /* Request with MeId=2, PipeId=0 */
> +               tmp = REG_SET_FIELD(0, CP_GFX_INDEX_MUTEX, REQUEST, 1);
> +               tmp = REG_SET_FIELD(tmp, CP_GFX_INDEX_MUTEX, CLIENTID, 4);
> +               WREG32_SOC15(GC, 0, regCP_GFX_INDEX_MUTEX, tmp);
> +               if (RREG32_SOC15(GC, 0, regCP_GFX_INDEX_MUTEX) == tmp)
> +                       break;
> +               udelay(1);
> +       }
> +
> +       if (i >= adev->usec_timeout) {
> +               printk("Failed to require the gfx mutex during soft reset\n");
> +               return -EINVAL;
> +       }
> +
>         WREG32_SOC15(GC, 0, regCP_VMID_RESET, 0xfffffffe);
>
>         // Read CP_VMID_RESET register three times.
> @@ -4526,6 +4542,10 @@ static int gfx_v11_0_soft_reset(void *handle)
>         RREG32_SOC15(GC, 0, regCP_VMID_RESET);
>         RREG32_SOC15(GC, 0, regCP_VMID_RESET);
>
> +       /* release the gfx mutex */
> +       tmp = REG_SET_FIELD(tmp, CP_GFX_INDEX_MUTEX, REQUEST, 0);
> +       WREG32_SOC15(GC, 0, regCP_GFX_INDEX_MUTEX, tmp);
> +
>         for (i = 0; i < adev->usec_timeout; i++) {
>                 if (!RREG32_SOC15(GC, 0, regCP_HQD_ACTIVE) &&
>                     !RREG32_SOC15(GC, 0, regCP_GFX_HQD_ACTIVE))
> --
> 2.41.0
>