Messages in this thread | | | Date | Tue, 4 Oct 2022 13:22:25 -0700 | Subject | Re: [PATCH 5/5] drm/dsc: Prevent negative BPG offsets from shadowing adjacent bitfields | From | Abhinav Kumar <> |
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On 10/1/2022 12:08 PM, 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@somainline.org> > --- > 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)); > } >
Looking at some examples of this for other vendors, they have managed to limit the value to 6 bits in their drivers:
https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/i915/display/intel_vdsc.c#L532
https://gitlab.freedesktop.org/drm/msm/-/blob/msm-next/drivers/gpu/drm/amd/display/dc/dsc/rc_calc_dpi.c#L87
Perhaps, msm should do the same thing instead of the helper change.
If you want to move to helper, other drivers need to be changed too to remove duplicate & 0x3f.
FWIW, this too has already been fixed in the latest downstream driver too.
Thanks
Abhinav
> /* PPS 88 */
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