linux-kernel - Re: [PATCH] drm/msm: UAPI error reporting

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Message-ID: <CAF6AEGtafQM7-mYy163Krry3OHgPNH3e9A=9VEhBpiQTADtULQ@mail.gmail.com>
Date: Fri, 22 Nov 2024 07:51:40 -0800
From: Rob Clark <robdclark@...il.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org, 
	freedreno@...ts.freedesktop.org, Rob Clark <robdclark@...omium.org>, 
	Sean Paul <sean@...rly.run>, Konrad Dybcio <konradybcio@...nel.org>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm: UAPI error reporting

On Fri, Nov 22, 2024 at 4:21 AM Konrad Dybcio
<konrad.dybcio@....qualcomm.com> wrote:
>
> On 21.11.2024 5:48 PM, Rob Clark wrote:
> > From: Rob Clark <robdclark@...omium.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@...omium.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