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

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Message-ID: <fb285034-ed4c-4f20-ab80-cf91d36fc67c@quicinc.com>
Date: Thu, 11 Jul 2024 11:03:15 -0700
From: Abhinav Kumar <quic_abhinavk@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn
 Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Jordan Crouse <jordan@...micpenguin.net>,
        Chandan Uddaraju <chandanu@...eaurora.org>,
        Rajesh Yadav
	<ryadav@...eaurora.org>,
        Sravanthi Kollukuduru <skolluku@...eaurora.org>,
        Archit Taneja <architt@...eaurora.org>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        Jeykumar Sankaran <jsanka@...eaurora.org>
Subject: Re: [PATCH 2/2] drm/msm/dpu: don't play tricks with debug macros



On 7/10/2024 12:40 AM, Dmitry Baryshkov wrote:
> On Tue, 9 Jul 2024 at 22:39, Abhinav Kumar <quic_abhinavk@...cinc.com> 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)
> 

Ack but we need to not just drop the wrappers but drop the usage of 
these macros as well because it is documented that they are deprecated.

So I assume you want to get this in and do that as a follow up change?

>>
>> /* 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.
> 

Alright, I am okay with the approach, just one minor suggestion, to keep 
the behavior intact, previously the code wanted DPU_DEBUG to be 
controlled by DRM_UT_KMS and DPU_DEBUG_DRIVER controlled by DRM_UT_DRIVER.

Keeping that intact, we need to use DRM_DEBUG_KMS for DPU_DEBUG?

>>
>>> Fixes: 25fdd5933e4c ("drm/msm: Add SDM845 DPU support")
>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>>> ---
>>>    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__)
>>>
> 
> 
>