linux-kernel - Re: [Freedreno] [PATCH] drm/msm/dp: Move debugfs files into subdirectory

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Date:   Sun, 17 Oct 2021 09:42:02 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     abhinavk@...eaurora.org
Cc:     Rob Clark <robdclark@...il.com>,
        Stephen Boyd <swboyd@...omium.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        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: [Freedreno] [PATCH] drm/msm/dp: Move debugfs files into
 subdirectory

On Fri 15 Oct 16:53 PDT 2021, abhinavk@...eaurora.org wrote:

> On 2021-10-15 16:17, Bjorn Andersson wrote:
> > In the cleanup path of the MSM DP driver the DP driver's debugfs files
> > are destroyed by invoking debugfs_remove_recursive() on debug->root,
> > which during initialization has been set to minor->debugfs_root.
> > 
> > To allow cleaning up the DP driver's debugfs files either each dentry
> > needs to be kept track of or the files needs to be put in a subdirectory
> > which can be removed in one go.
> > 
> > By choosing to put the debugfs files in a subdirectory, based on the
> > name of the associated connector this also solves the problem that these
> > names would collide as support for multiple DP instances are introduced.
> > 
> > One alternative solution to the problem with colliding file names would
> > have been to put keep track of the individual files and put them under
> > the connector's debugfs directory. But while the drm_connector has been
> > allocated, its associated debugfs directory has not been created at the
> > time of initialization of the dp_debug.
> > 
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> 
> I have been thinking about this problem ever since multi-DP has been posted
> :)
> Creating sub-directories seems right but at the moment it looks like IGT
> which
> uses these debugfs nodes doesnt check sub-directories:
> 
> https://gitlab.freedesktop.org/drm/igt-gpu-tools/-/blob/master/tools/msm_dp_compliance.c#L215
> 
> It looks for the DP debugfs nodes under /sys/kernel/debug/dri/*/
> 
> We have to fix IGT too to be able to handle multi-DP cases. I will try to
> come up
> with a proposal to address this.
> 
> Till then, can we go with the other solution to keep track of the dentries?
> 

I'm afraid I don't see what you're proposing.

Afaict we need one set of dp_test{type,active,data} per DP controller,
so even doing this by keeping track of the dentries requires that we
rename the files based on some identifier (id or connector name) - which
will cause igt to break.

As such, I think the practical path forward is that we merge the
multi-DP series as currently proposed. This will not cause any issues on
single-DP systems, but on multi-DP systems we will have warnings about
duplicate debugfs entries in the kernel logs.

Then you can figure out how to rework igt to deal with the multiple DP
instances and update the dp_debug interface accordingly.


Which also implies that we should hold this patch back. But if we go
that path, I think we should fix dp_debug_deinit() so that it doesn't
remove /sys/kernel/debug/dri/128 when the DP driver is unloaded.

Regards,
Bjorn

> > ---
> > 
> > This depends on
> > https://lore.kernel.org/linux-arm-msm/20211010030435.4000642-1-bjorn.andersson@linaro.org/
> > reducing the connector from a double pointer.
> > 
> >  drivers/gpu/drm/msm/dp/dp_debug.c | 15 +++++++++------
> >  1 file changed, 9 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/msm/dp/dp_debug.c
> > b/drivers/gpu/drm/msm/dp/dp_debug.c
> > index da4323556ef3..67da4c69eca1 100644
> > --- a/drivers/gpu/drm/msm/dp/dp_debug.c
> > +++ b/drivers/gpu/drm/msm/dp/dp_debug.c
> > @@ -210,26 +210,29 @@ static const struct file_operations
> > test_active_fops = {
> >  static int dp_debug_init(struct dp_debug *dp_debug, struct drm_minor
> > *minor)
> >  {
> >  	int rc = 0;
> > +	char path[64];
> >  	struct dp_debug_private *debug = container_of(dp_debug,
> >  			struct dp_debug_private, dp_debug);
> > 
> > -	debugfs_create_file("dp_debug", 0444, minor->debugfs_root,
> > +	snprintf(path, sizeof(path), "msm_dp-%s", debug->connector->name);
> > +
> > +	debug->root = debugfs_create_dir(path, minor->debugfs_root);
> > +
> > +	debugfs_create_file("dp_debug", 0444, debug->root,
> >  			debug, &dp_debug_fops);
> > 
> >  	debugfs_create_file("msm_dp_test_active", 0444,
> > -			minor->debugfs_root,
> > +			debug->root,
> >  			debug, &test_active_fops);
> > 
> >  	debugfs_create_file("msm_dp_test_data", 0444,
> > -			minor->debugfs_root,
> > +			debug->root,
> >  			debug, &dp_test_data_fops);
> > 
> >  	debugfs_create_file("msm_dp_test_type", 0444,
> > -			minor->debugfs_root,
> > +			debug->root,
> >  			debug, &dp_test_type_fops);
> > 
> > -	debug->root = minor->debugfs_root;
> > -
> >  	return rc;
> >  }