| Message ID | 20221001190807.358691-6-marijn.suijten@somainline.org (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | drm: Fix math issues in MSM DSC implementation | expand |
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@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)); 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 >
On Sat, 1 Oct 2022 at 23:23, Marijn Suijten <marijn.suijten@somainline.org> wrote: > > 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@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)); > > 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? This is definitely easier to review. However if you do not want to use FIELD_PREP, it would be better to split this into a series of `data |= something` assignments terminated with the rc_range_parameters[i] assignment. > > - Marijn > > > } > > > > /* PPS 88 */ > > -- > > 2.37.3 > >
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 */
On 2022-10-04 17:41:07, Dmitry Baryshkov wrote: > On Sat, 1 Oct 2022 at 23:23, Marijn Suijten > <marijn.suijten@somainline.org> wrote: > [..] > > 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? > > This is definitely easier to review. However if you do not want to use > FIELD_PREP, it would be better to split this into a series of `data |= > something` assignments terminated with the rc_range_parameters[i] > assignment. Anything is fine by me, I have no strong opinion on this and rather leave it up to the maintainers. However, FIELD_PREP gives us concise `#define`s through a single `GENMASK()` carrying both the shift and mask/field-width. At the same time these genmask definitions map more clearly to the layout comment right above: /* * For DSC sink programming the RC Range parameter fields * are as follows: Min_qp[15:11], max_qp[10:6], offset[5:0] */ If switching to `data |=` however, I've been recommended to not use FIELD_PREP but fulyl write out `data |= (value & MASK) << SHIFT` instead. Perhaps a more important question is how to apply this consistently throughout the function? - Marijn
On 2022-10-04 13:22:25, Abhinav Kumar wrote: > > 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. Thanks, I should have done my due-diligence and look up how other drivers dealt with this, but wasn't immediately expecting negative values elsewhere. Alas, as explained in the cover letter I opted to perform the masking in the PPS packing code as the DSC block code also reads these values, and would suddenly write 6-bit intead of 8-bit values to the DSC_RANGE_BPG_OFFSET registers. Quick testing on the mentioned sdm845 platform shows no regressions, but I'm not sure if that's safe to rely on? > If you want to move to helper, other drivers need to be changed too to > remove duplicate & 0x3f. Sure, we only have to confirm whether those drivers also read back the value(s) in rc_range_params, and expect / allow this to be 8 instead of 6 bits. > FWIW, this too has already been fixed in the latest downstream driver too. What is this supposed to mean? Is there a downstream DPU project that has pending patches needing to be upstreamed? Or is the downstream SDE, techpack/display, or whatever it is called nowadays, slowly using more DRM structs like drm_dsc_config and this drm_dsc_pps_payload_pack() helper function as pointed out in an earlier mail? Offtopic: are SDE and DPU growing closer together, hopefully achieving feature parity allowing the SDE project to be dropped in favour of a fully upstreamed DPU driver for day-one out-of-the-box mainline support for new SoCs (as long as work is published and on its way upstream)? - Marijn
On 10/4/2022 2:57 PM, Marijn Suijten wrote: > On 2022-10-04 13:22:25, Abhinav Kumar wrote: >> >> 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. > > Thanks, I should have done my due-diligence and look up how other > drivers dealt with this, but wasn't immediately expecting negative > values elsewhere. > > Alas, as explained in the cover letter I opted to perform the masking in > the PPS packing code as the DSC block code also reads these values, and > would suddenly write 6-bit intead of 8-bit values to the > DSC_RANGE_BPG_OFFSET registers. Quick testing on the mentioned sdm845 > platform shows no regressions, but I'm not sure if that's safe to rely > on? I looked up the MDP_DSC_0_RANGE_BPG_OFFSET_* registers. They take only a 6-bit value according to the SW documentation ( bits 5:0 ) It was always expecting only a 6-bit value and not 8. So this change is safe. > >> If you want to move to helper, other drivers need to be changed too to >> remove duplicate & 0x3f. > > Sure, we only have to confirm whether those drivers also read back the > value(s) in rc_range_params, and expect / allow this to be 8 instead of > 6 bits. > >> FWIW, this too has already been fixed in the latest downstream driver too. > > What is this supposed to mean? Is there a downstream DPU project that > has pending patches needing to be upstreamed? Or is the downstream SDE, > techpack/display, or whatever it is called nowadays, slowly using more > DRM structs like drm_dsc_config and this drm_dsc_pps_payload_pack() > helper function as pointed out in an earlier mail? > No, what I meant was, the version of downstream driver based on which the upstream DSC was made seems to be an older version. Downstream drivers keep getting updated and we always keep trying to align with upstream structs. This is true not just for DSC but even other blocks. So as part of that effort, we started using struct drm_dsc_config . That change was made on newer chipsets. But the downstream SW on sdm845 based on which the DSC was upstreamed seems like didnt have that. Hence all this redundant math happened. So this comment was more of a explanation about why this issue happened even though latest downstream didnt have this issue. > Offtopic: are SDE and DPU growing closer together, hopefully achieving > feature parity allowing the SDE project to be dropped in favour of a > fully upstreamed DPU driver for day-one out-of-the-box mainline support > for new SoCs (as long as work is published and on its way upstream)? > There is still a lot of gap between SDE and DPU drivers at this point. We keep trying to upstream as many features as possible to minimize the gap but there is still a lot of work to do. > - Marijn
On 2022-10-04 15:31:10, Abhinav Kumar wrote: > > > On 10/4/2022 2:57 PM, Marijn Suijten wrote: > > [..] > > Alas, as explained in the cover letter I opted to perform the masking in > > the PPS packing code as the DSC block code also reads these values, and > > would suddenly write 6-bit intead of 8-bit values to the > > DSC_RANGE_BPG_OFFSET registers. Quick testing on the mentioned sdm845 > > platform shows no regressions, but I'm not sure if that's safe to rely > > on? > > I looked up the MDP_DSC_0_RANGE_BPG_OFFSET_* registers. > They take only a 6-bit value according to the SW documentation ( bits 5:0 ) > > It was always expecting only a 6-bit value and not 8. > > So this change is safe. Ack, I think that implies I should make this change and move the masks to the DSI driver? > >> If you want to move to helper, other drivers need to be changed too to > >> remove duplicate & 0x3f. > > > > Sure, we only have to confirm whether those drivers also read back the > > value(s) in rc_range_params, and expect / allow this to be 8 instead of > > 6 bits. > > > >> FWIW, this too has already been fixed in the latest downstream driver too. > > > > What is this supposed to mean? Is there a downstream DPU project that > > has pending patches needing to be upstreamed? Or is the downstream SDE, > > techpack/display, or whatever it is called nowadays, slowly using more > > DRM structs like drm_dsc_config and this drm_dsc_pps_payload_pack() > > helper function as pointed out in an earlier mail? > > > > No, what I meant was, the version of downstream driver based on which > the upstream DSC was made seems to be an older version. Downstream > drivers keep getting updated and we always keep trying to align with > upstream structs. > > This is true not just for DSC but even other blocks. > > So as part of that effort, we started using struct drm_dsc_config . That > change was made on newer chipsets. But the downstream SW on sdm845 based > on which the DSC was upstreamed seems like didnt have that. Hence all > this redundant math happened. > > So this comment was more of a explanation about why this issue happened > even though latest downstream didnt have this issue. Thanks, I understood most of that but wasn't aware these exact "issues" were also addressed downstream (by i.e. also using the upstream structs). > > Offtopic: are SDE and DPU growing closer together, hopefully achieving > > feature parity allowing the SDE project to be dropped in favour of a > > fully upstreamed DPU driver for day-one out-of-the-box mainline support > > for new SoCs (as long as work is published and on its way upstream)? > > > > There is still a lot of gap between SDE and DPU drivers at this point. > We keep trying to upstream as many features as possible to minimize the > gap but there is still a lot of work to do. Glad to hear, but that sounds like a very hard to close gap unless downstream "just works on DPU" instead of having parallel development on two "competing" drivers for the exact same hardware. - Marijn
On 10/4/2022 3:39 PM, Marijn Suijten wrote: > On 2022-10-04 15:31:10, Abhinav Kumar wrote: >> >> >> On 10/4/2022 2:57 PM, Marijn Suijten wrote: >>> [..] >>> Alas, as explained in the cover letter I opted to perform the masking in >>> the PPS packing code as the DSC block code also reads these values, and >>> would suddenly write 6-bit intead of 8-bit values to the >>> DSC_RANGE_BPG_OFFSET registers. Quick testing on the mentioned sdm845 >>> platform shows no regressions, but I'm not sure if that's safe to rely >>> on? >> >> I looked up the MDP_DSC_0_RANGE_BPG_OFFSET_* registers. >> They take only a 6-bit value according to the SW documentation ( bits 5:0 ) >> >> It was always expecting only a 6-bit value and not 8. >> >> So this change is safe. > > Ack, I think that implies I should make this change and move the masks > to the DSI driver? hmm .... downstream seems to have the & just before the reg write https://git.codelinaro.org/clo/la/platform/vendor/opensource/display-drivers/-/blob/DISPLAY.LA.2.0.r1-08000-WAIPIO.0/msm/sde/sde_hw_dsc_1_2.c#L310 But yes, we can move this to the dsi calculation to match what others are doing. I am fine with that. > >>>> If you want to move to helper, other drivers need to be changed too to >>>> remove duplicate & 0x3f. >>> >>> Sure, we only have to confirm whether those drivers also read back the >>> value(s) in rc_range_params, and expect / allow this to be 8 instead of >>> 6 bits. >>> >>>> FWIW, this too has already been fixed in the latest downstream driver too. >>> >>> What is this supposed to mean? Is there a downstream DPU project that >>> has pending patches needing to be upstreamed? Or is the downstream SDE, >>> techpack/display, or whatever it is called nowadays, slowly using more >>> DRM structs like drm_dsc_config and this drm_dsc_pps_payload_pack() >>> helper function as pointed out in an earlier mail? >>> >> >> No, what I meant was, the version of downstream driver based on which >> the upstream DSC was made seems to be an older version. Downstream >> drivers keep getting updated and we always keep trying to align with >> upstream structs. >> >> This is true not just for DSC but even other blocks. >> >> So as part of that effort, we started using struct drm_dsc_config . That >> change was made on newer chipsets. But the downstream SW on sdm845 based >> on which the DSC was upstreamed seems like didnt have that. Hence all >> this redundant math happened. >> >> So this comment was more of a explanation about why this issue happened >> even though latest downstream didnt have this issue. > > Thanks, I understood most of that but wasn't aware these exact "issues" > were also addressed downstream (by i.e. also using the upstream > structs). > Even I wasnt. When I was reviewing this series, it seemed like a valid change so I checked the latest downstream code like i always do to see whether and how this is handled and found that these issues were addressed there so thought i would update that here. >>> Offtopic: are SDE and DPU growing closer together, hopefully achieving >>> feature parity allowing the SDE project to be dropped in favour of a >>> fully upstreamed DPU driver for day-one out-of-the-box mainline support >>> for new SoCs (as long as work is published and on its way upstream)? >>> >> >> There is still a lot of gap between SDE and DPU drivers at this point. >> We keep trying to upstream as many features as possible to minimize the >> gap but there is still a lot of work to do. > > Glad to hear, but that sounds like a very hard to close gap unless > downstream "just works on DPU" instead of having parallel development on > two "competing" drivers for the exact same hardware. > Its not really parallel development OR competing drivers. The design of these features downstream (not just DSC but many others) is quite different because some of the downstream designs wont get accepted upstream as its tightly coupled with our compositor/device-tree. Thats where we are slowly trying to implement these in an upstream compatible way. BTW, that being said. Its not always the case that every issue seen upstream has already been fixed downstream. In fact, on some occasions we found something fixed in upstream in a better way and ported them downstream too. Thanks Abhinav > - Marijn
On 2022-10-05 08:33:23, Abhinav Kumar wrote: [..] > hmm .... downstream seems to have the & just before the reg write > > https://git.codelinaro.org/clo/la/platform/vendor/opensource/display-drivers/-/blob/DISPLAY.LA.2.0.r1-08000-WAIPIO.0/msm/sde/sde_hw_dsc_1_2.c#L310 https://git.codelinaro.org/clo/la/platform/vendor/opensource/display-drivers/-/blob/DISPLAY.LA.2.0.r1-08000-WAIPIO.0/msm/sde/sde_hw_dsc.c#L156 The reference code for NON-v1.2 doesn't do this here, but you already confirmed by the docs - and I confirmed by testing a set of size #1 - that the register is fine with having only 6 bits. > But yes, we can move this to the dsi calculation to match what others > are doing. I am fine with that. Thanks, done that in v2. > > [..] > > Even I wasnt. When I was reviewing this series, it seemed like a valid > change so I checked the latest downstream code like i always do to see > whether and how this is handled and found that these issues were > addressed there so thought i would update that here. Thanks for confirming that it was done in the correct/same way :) > > [..] > Its not really parallel development OR competing drivers. > The design of these features downstream (not just DSC but many others) > is quite different because some of the downstream designs wont get > accepted upstream as its tightly coupled with our > compositor/device-tree. Thats where we are slowly trying to implement > these in an upstream compatible way. But this is what it feels like. To me this sounds like downstream is more of a staging / prototyping area that is actively used in production, while the driver implementation is fleshed out and slowly brought to mainline in a careful and controlled manner. That's not a bad thing, but it does mean that mainline always lags behind in terms of features and hardware support. At least I'm glad to hear that downstream is slowly using more DRM primitives, and the driver is becoming more digestible as well. > BTW, that being said. Its not always the case that every issue seen > upstream has already been fixed downstream. In fact, on some occasions > we found something fixed in upstream in a better way and ported them > downstream too. I wasn't expecting anything else, as different drivers have inevitably different details and different bugs. The issues this series fixes weren't applicable to the downstream kernel because it (at the time) wasn't even using this drm_dsc_config struct with different semantics. Regardless, it's good to hear that fixes are transplanted in both ways even if it does mean extra overhead maintaining and keeping tabs on two drivers at once. - Marijn
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)); } /* PPS 88 */
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(-)