linux-kernel - Re: [PATCH v2] drm/msm/dp: Only create debugfs for PRIMARY minor

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Date:   Mon, 20 Dec 2021 11:51:34 -0800
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Clark <robdclark@...il.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC:     Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        "Daniel Vetter" <daniel@...ll.ch>, <linux-arm-msm@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] drm/msm/dp: Only create debugfs for PRIMARY minor



On 12/16/2021 4:20 PM, Bjorn Andersson wrote:
> dpu_kms_debugfs_init() is invoked for each minor being registered. Most
> of the files created are unrelated to the minor, so there's no reason to
> present them per minor.
> The exception to this is the DisplayPort code, which ends up invoking
> dp_debug_get() for each minor, each time associate the allocated object
> with dp->debug.
> 
> As such dp_debug will create debugfs files in both the PRIMARY and the
> RENDER minor's debugfs directory, but only the last reference will be
> remembered.
> 
> The only use of this reference today is in the cleanup path in
> dp_display_deinit_sub_modules() and the dp_debug_private object does
> outlive the debugfs entries in either case, so there doesn't seem to be
> any adverse effects of this, but per the code the current behavior is
> unexpected, so change it to only create debugfs files for the PRIMARY
> minor.
> 
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
> 
> Changes since v1:
> - Moved the check up from msm_dp_debugfs_init() to dpu_kms_debugfs_init()
> 
>   drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> index 2ee70072a1b4..a54f7d373f14 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> @@ -193,6 +193,10 @@ static int dpu_kms_debugfs_init(struct msm_kms *kms, struct drm_minor *minor)
>   	if (!p)
>   		return -EINVAL;
>   
> +	/* Only create one set of debugfs per DP instance */
I would change this to DPU now instead of DP, but apart from that,

Reviewed-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
> +	if (minor->type != DRM_MINOR_PRIMARY)
> +		return 0;
> +
>   	dev = dpu_kms->dev;
>   	priv = dev->dev_private;
>