El lun, 01-06-2026 a las 16:13 -0300, Maíra Canal escribió: > A compute shader dispatch encodes its workgroup counts in the > CFG0..CFG2 > registers. Kicking off a dispatch with a zero count in any of the > three > dimensions is invalid. First, the hardware will process 0 as 65536, > causing an illegitimate submission. But over that, a submission with > a > zeroed workgroup dimension should be a no-op. > > These zeroed counts can reach the dispatch path through an indirect > CSD > job, whose workgroup counts are only known once the indirect buffer > is > read and may legitimately be zero, but such scenario should only > result in > a no-op. > > Don't submit the job to the hardware when any of the workgroup counts > is > zero, so the job completes immediately instead of running the shader. > > Cc: [email protected] > Fixes: d223f98f0209 ("drm/v3d: Add support for compute shader > dispatch.") > Suggested-by: Jose Maria Casanova Crespo <[email protected]> > Signed-off-by: Maíra Canal <[email protected]> > --- > drivers/gpu/drm/v3d/v3d_sched.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/drivers/gpu/drm/v3d/v3d_sched.c > b/drivers/gpu/drm/v3d/v3d_sched.c > index 47f83936cd73..681d10af4c8e 100644 > --- a/drivers/gpu/drm/v3d/v3d_sched.c > +++ b/drivers/gpu/drm/v3d/v3d_sched.c > @@ -352,6 +352,15 @@ v3d_csd_job_run(struct drm_sched_job *sched_job) > return NULL; > } > > + /* For dispatch dimensions, HW interprets 0 as 65536, > causing > + * illegitimate submissions that must be rejected. Note that > + * 65535 (2^16 - 1) is the maximum number of workgroups per > dimension. > + */
I am not sure this description is accurate. I think passing in 0 doesn't cause illegitimate submissions. I think the issue is that if we allow 0 to be interpreted as 65536 then can't tell if an indirect job actually configured 0 as the dimension. So I'd rephrase this as: /* The hw interprets a workgroup size of 0 as 65536, however, * the user-space driver exposes a maximum of 65535. So a 0 on any * dimension means that we have no workgroups and the compute shader * should not be dispatched. */ With that change, both patches are: Reviewed-by: Iago Toral Quiroga <[email protected]> > + if (!V3D_GET_FIELD(job->args.cfg[0], > V3D_CSD_QUEUED_CFG0_NUM_WGS_X) || > + !V3D_GET_FIELD(job->args.cfg[1], > V3D_CSD_QUEUED_CFG1_NUM_WGS_Y) || > + !V3D_GET_FIELD(job->args.cfg[2], > V3D_CSD_QUEUED_CFG2_NUM_WGS_Z)) > + return NULL; > + > v3d->queue[V3D_CSD].active_job = &job->base; > > v3d_invalidate_caches(v3d); >
