[PATCH] drm/msm: UAPI error reporting

[Rob Clark]

On Fri, Nov 22, 2024 at 4:21 AM Konrad Dybcio
<konrad.dybcio at oss.qualcomm.com> wrote:
>
> On 21.11.2024 5:48 PM, Rob Clark wrote:
> > From: Rob Clark <robdclark at chromium.org>
> >
> > Debugging incorrect UAPI usage tends to be a bit painful, so add a
> > helper macro to make it easier to add debug logging which can be enabled
> > at runtime via drm.debug.
> >
> > Signed-off-by: Rob Clark <robdclark at chromium.org>
> > ---
>
> [...]
>
> > +/* Helper for returning a UABI error with optional logging which can make
> > + * it easier for userspace to understand what it is doing wrong.
> > + */
> > +#define UERR(err, drm, fmt, ...) \
> > +     ({ DRM_DEV_DEBUG_DRIVER((drm)->dev, fmt, ##__VA_ARGS__); -(err); })
> > +
> >  #define DBG(fmt, ...) DRM_DEBUG_DRIVER(fmt"\n", ##__VA_ARGS__)
> >  #define VERB(fmt, ...) if (0) DRM_DEBUG_DRIVER(fmt"\n", ##__VA_ARGS__)
>
> I'm generally not a fan of adding driver-specific debug prints..
>
> Maybe that's something that could be pushed to the drm-common layer
> or even deeper down the stack?

Even if we had something like DRM_DBG_UABI_ERROR() I'd probably still
just #define UERR() to be a wrapper for it, since line length/wrapping
tends to be a bit of a challenge.  And I have a fairly substantial
patch stack on top of this adding sparse/vm_bind support.  (Debugging
that was actually the motivation for this patch.)

I noticed that xe has something similar, but slightly different shape,
in the form of XE_IOCTL_DBG().. but that kinda just moves the line
length problem into the if() conditional.  (And doesn't provide the
benefit of being able to display the incorrect param.)

BR,
-R