On 10/9/2024 4:15 PM, Kandpal, Suraj wrote:
-----Original Message-----
From: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
Sent: Wednesday, October 9, 2024 3:30 PM
To: Kandpal, Suraj <suraj.kandpal@xxxxxxxxx>; intel-
xe@xxxxxxxxxxxxxxxxxxxxx; intel-gfx@xxxxxxxxxxxxxxxxxxxxx
Cc: Nautiyal, Ankit K <ankit.k.nautiyal@xxxxxxxxx>; Kandpal, Suraj
<suraj.kandpal@xxxxxxxxx>
Subject: Re: [PATCH] drm/i915/dp_mst: Fix dsc mst bw overhead calculation
On Wed, 09 Oct 2024, Suraj Kandpal <suraj.kandpal@xxxxxxxxx> wrote:
Fix the DSC flag assignment based on the dsc_slice_count returned to
avoid divide by zero error.
Fixes: 4e0837a8d00a ("drm/i915/dp_mst: Account for FEC and DSC
overhead during BW allocation")
Signed-off-by: Suraj Kandpal <suraj.kandpal@xxxxxxxxx>
---
drivers/gpu/drm/i915/display/intel_dp_mst.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c
b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 4765bda154c1..bacd294d6bb6 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -105,11 +105,16 @@ static int intel_dp_mst_bw_overhead(const
struct intel_crtc_state *crtc_state,
if (dsc) {
int num_joined_pipes =
intel_crtc_num_joined_pipes(crtc_state);
- flags |= DRM_DP_BW_OVERHEAD_DSC;
dsc_slice_count = intel_dp_dsc_get_slice_count(connector,
adjusted_mode-
clock,
adjusted_mode-
hdisplay,
num_joined_pipes);
+ /*
+ * Try with dsc only if dsc_slice_count has a sane value i.e
value is no
+ * 0
+ */
+ if (dsc_slice_count)
+ flags |= DRM_DP_BW_OVERHEAD_DSC;
Do you think that's enough to handle the error?!
Well this will make sure that if dsc_slice_count ends up being zero we don't take dsc overhead into account.
Which should be enough to make sure we don't go and end up having a divide by zero error
But the overhead computed will not be correct. I was thinking to avoid
setting dsc flag if we dont get a valid slice_count.
Perhaps in intel_dp_dsc_mst_compute_link_config() before calling
intel_dp_mst_find_vcpi_slots_for_bpp() we should check for slice_count.
Actually we again compute dsc slice_count quite late in
dp_dsc_compute_config and set that in pipe_config->dsc.slice_count .
Regards,
Ankit
Regards,
Suraj Kandpal
BR,
Jani.
}
overhead = drm_dp_bw_overhead(crtc_state->lane_count,
--
Jani Nikula, Intel
