[PATCH v5 02/16] drm/msm/dpu: fix error condition in dpu_encoder_virt_atomic_mode_set

[Dmitry Baryshkov]

On Sat, 13 Jul 2024 at 03:25, Abhinav Kumar <quic_abhinavk at quicinc.com> wrote:
>
>
>
> On 7/12/2024 4:11 PM, Dmitry Baryshkov wrote:
> > On Fri, 12 Jul 2024 at 22:41, Abhinav Kumar <quic_abhinavk at quicinc.com> wrote:
> >> On 6/24/2024 2:13 PM, Dmitry Baryshkov wrote:
> >>> The commit b954fa6baaca ("drm/msm/dpu: Refactor rm iterator") removed
> >>> zero-init of the hw_ctl array, but didn't change the error condition,
> >>> that checked for hw_ctl[i] being NULL. Use indices check instead.
> >>>
> >>> Fixes: b954fa6baaca ("drm/msm/dpu: Refactor rm iterator")
> >>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
> >>> ---
> >>>    drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 2 +-
> >>>    1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> >>> index 5d205e09cf45..7613005fbfea 100644
> >>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> >>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> >>> @@ -1186,7 +1186,7 @@ static void :tag(struct drm_encoder *drm_enc,
> >>>                        return;
> >>>                }
> >>>
> >>> -             if (!hw_ctl[i]) {
> >>> +             if (i >= num_ctl) {
> >>
> >> This is not very clear to me.
> >>
> >> How will we hit this condition? I dont see i going beyond 1 in this loop
> >> and neither should num_ctl
> >
> > Why? the driver doesn't support flushing through a single CTL, so
> > num_ctl = num_intf.
> >
>
> num_ctl will be = num_intf, but what I was trying to understand here is
> that , previously this condition was making sure that we have a ctl
> assigned for each physical encoder which is actually a requirement for
> the display pipeline. If we assigned a hw_ctl for one phys encoder and
> not the other, its an error.
>
> But on closer look, I think even your check will catch that.
>
>
> >>
> >> Will it be just easier to bring back the NULL assignment at the top?
> >>
> >> struct dpu_hw_blk *hw_ctl[MAX_CHANNELS_PER_ENC] = { NULL };
> >>
> >> I also see the same issue for other blocks such as hw_dsc, hw_lm
> >
> > Other blocks loop properly up to the num_resource. I'd prefer to drop
> > the NULL init from the DSPP init and use num_dspp instead.
> >
>
> Overall, I think the purpose of NULL init was to make sure that before
> we call to_dpu_hw_***() macros, we have a valid hw_*.
>
> We could use either num_* or the hw_* as both are returned by RM.
>
> One side-note here is with a proper NULL hw_ctl is that the consumers of
> hw_ctl should also be able to check for NULL correctly.

The problem of the NULL checks is that it's too tempting to perform a
NULL check after to_dpu_hw_ctl conversion. However it's not safe to
pass NULL pointer to such functions: there is no guarantee that
conversion will return NULL if it gets passed the NULL pointer.

> So for example dpu_encoder_phys layers use if (!phys->hw_ctl) checks but
> today we do not set phys->hw_ctl to NULL correctly.
>
> Do you think that instead of the return statements, we should do
> something like
>
> dpu_enc->hw_ctl = i < num_ctl ?
>         to_dpu_hw_ctl(hw_ctl[i]) : NULL;

Yeah, why not.

Generally, I think we should stop storing the state-related data in
the non-state structures. Hopefully I'll have time for that at some
point later on.

>
>
> But this will need the NULL init back.

It doesn't, as you have the comparison.

>
> >>
> >>>                        DPU_ERROR_ENC(dpu_enc,
> >>>                                "no ctl block assigned at idx: %d\n", i);
> >>>                        return;
> >>>
> >
> >
> >



-- 
With best wishes
Dmitry