Re: [PATCH 2/2] drm/msm/dpu: don't play tricks with debug macros

[Dmitry Baryshkov]

On Tue, 9 Jul 2024 at 22:39, Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx> wrote:
>
>
>
> On 7/9/2024 6:48 AM, Dmitry Baryshkov wrote:
> > DPU debugging macros need to be converted to a proper drm_debug_*
> > macros, however this is a going an intrusive patch, not suitable for a
> > fix. Wire DPU_DEBUG and DPU_DEBUG_DRIVER to always use DRM_DEBUG_DRIVER
> > to make sure that DPU debugging messages always end up in the drm debug
> > messages and are controlled via the usual drm.debug mask.
> >
>
> These macros have been deprecated, is this waht you meant by the
> conversion to proper drm_debug_*?

Yes. Drop the driver-specific wrappers where they don't make sense.
Use sensible format strings in the cases where it actually does (like
VIDENC or _PLANE)

>
> /* NOTE: this is deprecated in favor of drm_dbg(NULL, ...). */
> #define DRM_DEBUG_DRIVER(fmt, ...)                                      \
>          __drm_dbg(DRM_UT_DRIVER, fmt, ##__VA_ARGS__)
>
> I think all that this macro was doing was to have appropriate DRM_UT_*
> macros enabled before calling the corresponding DRM_DEBUG_* macros. But
> I think what was incorrect here is for DPU_DEBUG, we could have used
> DRM_UT_CORE instead of DRM_UT_KMS.

It pretty much tries to overplay the existing drm debugging mechanism
by either sending the messages to the DRM channel or just using
pr_debug. With DYNAMIC_DEBUG being disabled pr_debug is just an empty
macro, so all the messages can end up in /dev/null. We should not be
trying to be too smart, using standard DRM_DEBUG_DRIVER should be
enough. This way all driver-related messages are controlled by
drm.debug including or excluding the 0x02 bit.


>
> And DRM_DEBUG_DRIVER should have been used instead of DRM_ERROR.
>
> Was this causing the issue of the prints not getting enabled?

I pretty much think so.

>
> > Fixes: 25fdd5933e4c ("drm/msm: Add SDM845 DPU support")
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h | 14 ++------------
> >   1 file changed, 2 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> > index e2adc937ea63..935ff6fd172c 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.h
> > @@ -31,24 +31,14 @@
> >    * @fmt: Pointer to format string
> >    */
> >   #define DPU_DEBUG(fmt, ...)                                                \
> > -     do {                                                               \
> > -             if (drm_debug_enabled(DRM_UT_KMS))                         \
> > -                     DRM_DEBUG(fmt, ##__VA_ARGS__); \
> > -             else                                                       \
> > -                     pr_debug(fmt, ##__VA_ARGS__);                      \
> > -     } while (0)
> > +     DRM_DEBUG_DRIVER(fmt, ##__VA_ARGS__)
> >
> >   /**
> >    * DPU_DEBUG_DRIVER - macro for hardware driver logging
> >    * @fmt: Pointer to format string
> >    */
> >   #define DPU_DEBUG_DRIVER(fmt, ...)                                         \
> > -     do {                                                               \
> > -             if (drm_debug_enabled(DRM_UT_DRIVER))                      \
> > -                     DRM_ERROR(fmt, ##__VA_ARGS__); \
> > -             else                                                       \
> > -                     pr_debug(fmt, ##__VA_ARGS__);                      \
> > -     } while (0)
> > +     DRM_DEBUG_DRIVER(fmt, ##__VA_ARGS__)
> >
> >   #define DPU_ERROR(fmt, ...) pr_err("[dpu error]" fmt, ##__VA_ARGS__)
> >   #define DPU_ERROR_RATELIMITED(fmt, ...) pr_err_ratelimited("[dpu error]" fmt, ##__VA_ARGS__)
> >



-- 
With best wishes
Dmitry