Re: [Intel-gfx] [RFC PATCH 4/5] drm/i915/display: prepend connector name to the backlight

[Jani Nikula <jani.nikula@intel.com>]

On Tue, 21 Jun 2022, "Murthy, Arun R" <arun.r.murthy@intel.com> wrote:
>> On Fri, 03 Jun 2022, "Murthy, Arun R" <arun.r.murthy@intel.com> wrote:
>> >> On Thu, 02 Jun 2022, Animesh Manna <animesh.manna@intel.com>
>> wrote:
>> >> > From: Arun R Murthy <arun.r.murthy@intel.com>
>> >> >
>> >> > With the enablement of dual eDP, there will have to exist two
>> >> > entries of backlight sysfs file. In order to avoid sysfs file name
>> >> > duplication, the file names are prepended with the connector name.
>> >>
>> >> Fixed by 20f85ef89d94 ("drm/i915/backlight: use unique backlight
>> >> device
>> >> names") about a year ago.
>> >>
>> > This patches checks if the return value is -EEXIST and then acts accordingly,
>> but -EEXIST is not returned.
>> > struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
>> >                                          const char *name,
>> >                                          umode_t mode, kuid_t uid, kgid_t gid,
>> >                                          loff_t size,
>> >                                          const struct kernfs_ops *ops,
>> >                                          void *priv, const void *ns,
>> >                                          struct lock_class_key *key) {
>> >         struct kernfs_node *kn;
>> >         unsigned flags;
>> >         int rc;
>> >
>> >         flags = KERNFS_FILE;
>> >
>> >         kn = kernfs_new_node(parent, name, (mode & S_IALLUGO) | S_IFREG,
>> >                              uid, gid, flags);
>> >         if (!kn)
>> >                 return ERR_PTR(-ENOMEM);
>> >
>> > So the condition check with not be satisfied and the backlight registration
>> will fail for the 2nd backlight device.
>>
>> But the file isn't added by kernfs_new_node(), it just allocates the node. See
>> the kernfs_add_one() later in __kernfs_create_file().
>>
> Moreover now that we will be supporting dual display, wouldn't it
> be better to have the same file naming convention for both the
> displays?
> Without this patch, the first backlight would create an interface
> with name intel_backlight and for the second it would create as
> "cardXX-XXX-backlight". There wont be any similarities in the
> backlight naming convention.
> Would it be better to maintain the same naming convention
> across the displays?

The old name can't be changed.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center