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Date: Tue, 22 Feb 2022 15:47:26 -0800 From: Doug Anderson <dianders@...omium.org> To: Javier Martinez Canillas <javierm@...hat.com> Cc: Jani Nikula <jani.nikula@...ux.intel.com>, Andrzej Hajda <andrzej.hajda@...el.com>, Neil Armstrong <narmstrong@...libre.com>, David Airlie <airlied@...ux.ie>, Robert Foss <robert.foss@...aro.org>, dri-devel <dri-devel@...ts.freedesktop.org>, Jonas Karlman <jonas@...boo.se>, LKML <linux-kernel@...r.kernel.org>, Jernej Skrabec <jernej.skrabec@...il.com>, Thierry Reding <thierry.reding@...il.com>, Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Thomas Zimmermann <tzimmermann@...e.de>, lschyi@...omium.org, Sam Ravnborg <sam@...nborg.org>, jjsu@...omium.org Subject: Re: [PATCH v2 2/3] drm: Plumb debugfs_init through to panels Hi, On Wed, Feb 16, 2022 at 1:36 AM Javier Martinez Canillas <javierm@...hat.com> wrote: > > On 2/16/22 10:25, Jani Nikula wrote: > > [snip] > > >> > >> I actually wrote said follow-up patches and they were ready to go, but > >> when I was trying to come up with the right "Fixes" tag I found commit > >> b792e64021ec ("drm: no need to check return value of debugfs_create > >> functions"). So what's being requested is nearly the opposite of what > >> Greg did there. > >> > >> I thought about perhaps only checking for directories but even that > >> type of check was removed by Greg's patch. Further checking shows that > >> start_creating() actually has: > >> > >> if (IS_ERR(parent)) > >> return parent; > >> > >> ...so I guess that explains why it's fine to skip the check even for parents? > >> > >> Sure enough I confirmed that if I pass `ERR_PTR(-EINVAL)` as the root > >> for `panel->funcs->debugfs_init()` that nothing bad seems to happen... > > > > Yeah, the idea is that you don't need to check for debugfs function > > return values and you can safely pass error pointers to debugfs > > functions. The worst that can happen is you don't get the debugfs, but > > hey, it's debugfs so you shouldn't fail anything else because of that > > anyway. > > > > Thanks a lot Doug and Jani for the explanations. That makes sense and it > explains why most code I looked was not checking for the return value. > > I guess we should write something about this in the debugfs functions > kernel doc so it's mentioned explicitly and people don't have to guess. For anyone interested, I've taken Javier's suggestion and tried to update the docs: https://lore.kernel.org/r/20220222154555.1.I26d364db7a007f8995e8f0dac978673bc8e9f5e2@changeid
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