Re: [Intel-gfx] [PATCH v5 4/5] drm/i915/display: consider DG2_RC_CCS_CC when migrating buffers

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Oct 04, 2022 at 02:19:15PM +0100, Matthew Auld wrote:
> For these types of display buffers, we need to able to CPU access some
> part of the backing memory in prepare_plane_clear_colors(). As a result
> we need to ensure we always place in the mappable part of lmem, which
> becomes necessary on small-bar systems.
> 
> v2(Nirmoy & Ville):
>  - Add some commentary for why we need to CPU access the buffer.
>  - Split out the other changes, so we just consider the display change
>    here.
> v3:
>  - Handle this in the dpt path.
> v4(Ville):
>  - Drop the intel_fb_rc_ccs_cc_plane() sanity check in
>    pin_and_fence_fb_obj(), since we can also trigger this on DG1 it
>    seems.

On some hw I think there was also a chicken bit to disable DPT,
and the DPT simulation situation was always a mess (you had
to enable it using some custom config). So in theory someone
might have the need to use the non-DPT path on more modern hw
as well, but I'm OK not considering it here. If someone thinks
that small-bar+no-DPT is important they can deal with it in a 
separate patch.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> 
> Fixes: eb1c535f0d69 ("drm/i915: turn on small BAR support")
> Reported-by: Jianshui Yu <jianshui.yu@intel.com>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Nirmoy Das <nirmoy.das@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_fb_pin.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_fb_pin.c b/drivers/gpu/drm/i915/display/intel_fb_pin.c
> index 5031ee5695dd..e12339f46640 100644
> --- a/drivers/gpu/drm/i915/display/intel_fb_pin.c
> +++ b/drivers/gpu/drm/i915/display/intel_fb_pin.c
> @@ -50,7 +50,18 @@ intel_pin_fb_obj_dpt(struct drm_framebuffer *fb,
>  			continue;
>  
>  		if (HAS_LMEM(dev_priv)) {
> -			ret = i915_gem_object_migrate(obj, &ww, INTEL_REGION_LMEM_0);
> +			unsigned int flags = obj->flags;
> +
> +			/*
> +			 * For this type of buffer we need to able to read from the CPU
> +			 * the clear color value found in the buffer, hence we need to
> +			 * ensure it is always in the mappable part of lmem, if this is
> +			 * a small-bar device.
> +			 */
> +			if (intel_fb_rc_ccs_cc_plane(fb) >= 0)
> +				flags &= ~I915_BO_ALLOC_GPU_ONLY;
> +			ret = __i915_gem_object_migrate(obj, &ww, INTEL_REGION_LMEM_0,
> +							flags);
>  			if (ret)
>  				continue;
>  		}
> -- 
> 2.37.3

-- 
Ville Syrjälä
Intel