From a122243367a4f9cea5c220d946a7f728e17622a2 Mon Sep 17 00:00:00 2001 From: Stanislav Lisovskiy Date: Thu, 29 Jun 2023 15:25:34 +0300 Subject: [PATCH] drm/i915: Fail if DSC compression requirement is less than platform supports Currently we just clamp that value to the highest supported one, however that means, we are not able to fit this into our available bandwidth range, so we might see glitches or FIFO underruns. While choosing less compressed bpp than min bpp required to handle the mode is harmless and might even save some bandwidth, choosing higher compressed bpp than min bpp required to handle the required mode config, can cause issues. So in that case lets just conclude that even with DSC, we are not able to comply with bandwidth requirements and fail. v2: - s/clamp_t/min_t/ (Luca Coelho) Signed-off-by: Stanislav Lisovskiy Reviewed-by: Luca Coelho Link: https://patchwork.freedesktop.org/patch/msgid/20230629122534.8815-1-stanislav.lisovskiy@intel.com --- drivers/gpu/drm/i915/display/intel_dp.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c index 09dc6c88ad28e..def5d8a98b401 100644 --- a/drivers/gpu/drm/i915/display/intel_dp.c +++ b/drivers/gpu/drm/i915/display/intel_dp.c @@ -713,9 +713,18 @@ u32 intel_dp_dsc_nearest_valid_bpp(struct drm_i915_private *i915, u32 bpp, u32 p /* * According to BSpec, 27 is the max DSC output bpp, - * 8 is the min DSC output bpp + * 8 is the min DSC output bpp. + * While we can still clamp higher bpp values to 27, saving bandwidth, + * if it is required to oompress up to bpp < 8, means we can't do + * that and probably means we can't fit the required mode, even with + * DSC enabled. */ - bits_per_pixel = clamp_t(u32, bits_per_pixel, 8, 27); + if (bits_per_pixel < 8) { + drm_dbg_kms(&i915->drm, "Unsupported BPP %u, min 8\n", + bits_per_pixel); + return 0; + } + bits_per_pixel = min_t(u32, bits_per_pixel, 27); } else { /* Find the nearest match in the array of known BPPs from VESA */ for (i = 0; i < ARRAY_SIZE(valid_dsc_bpp) - 1; i++) { -- 2.30.2