[PATCH 6/7] drm/i915/dp: Ensure hactive is divisible by slice count

[Ankit Nautiyal]

According to the DSC spec, the slice width should be chosen such that
the picture width (hactive) is evenly divisible by the slice width.
If not, extra pixels (padding) must be added to the last slice to
ensure all slices have the same width.

Currently, we do not support handling these extra pixels.
Therefore, select a slice count that evenly divides the hactive
(slice_width = hactive / slice_count).

This check is already implemented for DSI, where the slice count is
selected from the BIOS.

For DP, currently with 1, 2, 4 slices per pipe it is unlikely to have
slice count not being able to divide hactive, but with 3 DSC engines
and 3 slices, we can have such cases. Adding this check prepares for
future scenarios where such configurations might be used.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index dbb1d75c0576..d7d42eac4be3 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -1038,6 +1038,9 @@ u8 intel_dp_dsc_get_slice_count(const struct intel_connector *connector,
 		if (num_joined_pipes > 1 && valid_dsc_slicecount[i] < 2)
 			continue;
 
+		if (mode_hdisplay % test_slice_count)
+			continue;
+
 		if (min_slice_count <= test_slice_count)
 			return test_slice_count;
 	}
-- 
2.45.2