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

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Message-ID: <5ff5d720-ccf7-42ee-9a4b-90cc168a4b7b@oss.qualcomm.com>
Date: Sat, 23 Nov 2024 01:19:37 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Rob Clark <robdclark@...il.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 22.11.2024 4:51 PM, Rob Clark wrote:
> 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.)

Alright, let's not get in the way then

> 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.)

Maybe rust comes one day and the lines will start growing vertically ;)

Konrad