On 2022-10-01 21:08:07, Marijn Suijten wrote: > msm's dsi_host specifies negative BPG offsets which fill the full 8 bits > of a char thanks to two's complement: this however results in those bits > bleeding into the next parameter when the field is only expected to > contain 6-bit wide values. > As a consequence random slices appear corrupted on-screen (tested on a > Sony Tama Akatsuki device with sdm845). > > Use AND operators to limit all values that constitute the RC Range > parameter fields to their expected size. > > Fixes: b9080324d6ca ("drm/msm/dsi: add support for dsc data") > Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx> > --- > drivers/gpu/drm/display/drm_dsc_helper.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/display/drm_dsc_helper.c b/drivers/gpu/drm/display/drm_dsc_helper.c > index c869c6e51e2b..2e7ef242685d 100644 > --- a/drivers/gpu/drm/display/drm_dsc_helper.c > +++ b/drivers/gpu/drm/display/drm_dsc_helper.c > @@ -243,11 +243,11 @@ void drm_dsc_pps_payload_pack(struct drm_dsc_picture_parameter_set *pps_payload, > */ > for (i = 0; i < DSC_NUM_BUF_RANGES; i++) { > pps_payload->rc_range_parameters[i] = > - cpu_to_be16((dsc_cfg->rc_range_params[i].range_min_qp << > + cpu_to_be16(((dsc_cfg->rc_range_params[i].range_min_qp & 0x1f) << > DSC_PPS_RC_RANGE_MINQP_SHIFT) | > - (dsc_cfg->rc_range_params[i].range_max_qp << > + ((dsc_cfg->rc_range_params[i].range_max_qp & 0x1f) << > DSC_PPS_RC_RANGE_MAXQP_SHIFT) | > - (dsc_cfg->rc_range_params[i].range_bpg_offset)); > + (dsc_cfg->rc_range_params[i].range_bpg_offset & 0x3f)); Pre-empting the reviews: I was contemplating whether to use FIELD_PREP here, given that it's not yet used anywhere else in this file. For that I'd remove the existing _SHIFT definitions and replace them with: #define DSC_PPS_RC_RANGE_MINQP_MASK GENMASK(15, 11) #define DSC_PPS_RC_RANGE_MAXQP_MASK GENMASK(10, 6) #define DSC_PPS_RC_RANGE_BPG_OFFSET_MASK GENMASK(5, 0) And turn this section of code into: cpu_to_be16(FIELD_PREP(DSC_PPS_RC_RANGE_MINQP_MASK, dsc_cfg->rc_range_params[i].range_min_qp) | FIELD_PREP(DSC_PPS_RC_RANGE_MAXQP_MASK, dsc_cfg->rc_range_params[i].range_max_qp) | FIELD_PREP(DSC_PPS_RC_RANGE_BPG_OFFSET_MASK, dsc_cfg->rc_range_params[i].range_bpg_offset)); Is that okay/recommended? - Marijn > } > > /* PPS 88 */ > -- > 2.37.3 >