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Wed, 16 Feb 2022 11:42:56 +0000 Received: from DM6PR11MB3180.namprd11.prod.outlook.com ([fe80::11f6:76fa:fc62:6511]) by DM6PR11MB3180.namprd11.prod.outlook.com ([fe80::11f6:76fa:fc62:6511%6]) with mapi id 15.20.4995.016; Wed, 16 Feb 2022 11:42:56 +0000 Message-ID: <68332eba-800a-544a-846b-f59ff694c915@intel.com> Date: Wed, 16 Feb 2022 12:42:50 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Firefox/91.0 Thunderbird/91.6.0 Subject: Re: [PATCH v2 2/3] drm: Plumb debugfs_init through to panels Content-Language: en-US To: Javier Martinez Canillas , Jani Nikula , Doug Anderson CC: Laurent Pinchart , Jonas Karlman , David Airlie , Robert Foss , Neil Armstrong , "Jernej Skrabec" , LKML , Thierry Reding , dri-devel , Thomas Zimmermann , , Sam Ravnborg , References: <20220205001342.3155839-1-dianders@chromium.org> <20220204161245.v2.2.Ib0bd5346135cbb0b63006b69b61d4c8af6484740@changeid> <5d60473d-be8f-e2dc-2ce9-bc0b9056e4b4@redhat.com> <87ee435fjs.fsf@intel.com> From: Andrzej Hajda Organization: Intel Technology Poland sp. z o.o. - ul. 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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,