Re: [PATCH v2 2/3] drm: Plumb debugfs_init through to panels

[Andrzej Hajda]

On 16.02.2022 10:35, Javier Martinez Canillas 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.

Nice, didn't know debugfs started using this pattern. I hope the pattern 
will be used broader, as it allows to save lot of redundant checks.

Regards
Andrzej


> Best regards,