[Intel-gfx] [PATCH v4 2/5] drm/i915/guc: Wait for ucode DMA transfer completion

[Chris Wilson]

Quoting Michal Wajdeczko (2017-11-03 15:18:13)
> We silently assumed that DMA transfer will be completed
> within assumed timeout and thus we were waiting only at
> last step for GuC to become ready. Add intermediate wait
> to catch unexpected delays in DMA transfer.
> 
> Signed-off-by: Michal Wajdeczko <michal.wajdeczko at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Sagar Arun Kamble <sagar.a.kamble at intel.com>
> Reviewed-by: Sagar Arun Kamble <sagar.a.kamble at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_guc_fw.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_guc_fw.c b/drivers/gpu/drm/i915/intel_guc_fw.c
> index c4f4526..74a61fe 100644
> --- a/drivers/gpu/drm/i915/intel_guc_fw.c
> +++ b/drivers/gpu/drm/i915/intel_guc_fw.c
> @@ -160,6 +160,8 @@ static int guc_xfer_ucode(struct intel_guc *guc, struct i915_vma *vma)
>         struct drm_i915_private *dev_priv = guc_to_i915(guc);
>         struct intel_uc_fw *guc_fw = &guc->fw;
>         unsigned long offset;
> +       u32 status;
> +       int ret;
>  
>         /*
>          * The header plus uCode will be copied to WOPCM via DMA, excluding any
> @@ -182,7 +184,12 @@ static int guc_xfer_ucode(struct intel_guc *guc, struct i915_vma *vma)
>         /* Finally start the DMA */
>         I915_WRITE(DMA_CTRL, _MASKED_BIT_ENABLE(UOS_MOVE | START_DMA));
>  
> -       return 0;
> +       /* Wait for DMA to finish */
> +       ret = __intel_wait_for_register_fw(dev_priv, DMA_CTRL, START_DMA, 0,
> +                                          2, 100, &status);

To use _fw, you need to either hold forcewake or be sure you don't need
it, and you also need to be sure that either you have serialisation
around the routine or that it is not subject to the various concurrent
mmio access bugs. I haven't seen anything that suggests they have been
taken into account.
-Chris