Re: [PATCH v2] backlight: turn backlight on/off when necessary

[Liu Ying <Ying.Liu@freescale.com>]

On 01/23/2014 05:27 PM, Liu Ying wrote:
> On 01/23/2014 01:44 PM, Jingoo Han wrote:
>> On Wednesday, January 22, 2014 6:36 PM, Jani Nikula wrote:
>>> On Mon, 20 Jan 2014, Liu Ying <Ying.Liu@freescale.com> wrote:
>>>> We don't have to turn backlight on/off everytime a blanking
>>>> or unblanking event comes because the backlight status may
>>>> have already been what we want. Another thought is that one
>>>> backlight device may be shared by multiple framebuffers. We
>>>> don't hope blanking one of the framebuffers may turn the
>>>> backlight off for all the other framebuffers, since they are
>>>> likely being active to display something. This patch adds
>>>> some logics to record each framebuffer's backlight usage to
>>>> determine the backlight device use count and whether the
>>>> backlight should be turned on or off. To be more specific,
>>>> only one unblank operation on a certain blanked framebuffer
>>>> may increase the backlight device's use count by one, while
>>>> one blank operation on a certain unblanked framebuffer may
>>>> decrease the use count by one, because the userspace is
>>>> likely to unblank a unblanked framebuffer or blank a blanked
>>>> framebuffer.
>>>>
>>>> Signed-off-by: Liu Ying <Ying.Liu@freescale.com>
>>>> ---
>>>> v1 can be found at https://lkml.org/lkml/2013/5/30/139
>>>>
>>>> v1->v2:
>>>> * Make the commit message be more specific about the condition
>>>>   in which backlight device use count can be increased/decreased.
>>>> * Correct the setting for bd->props.fb_blank.
>>>>
>>>>  drivers/video/backlight/backlight.c |   28 +++++++++++++++++++++-------
>>>>  include/linux/backlight.h           |    6 ++++++
>>>>  2 files changed, 27 insertions(+), 7 deletions(-)
>>>>
>>
>> [.....]
>>>
>>> Anything backlight worries me a little, and there are actually three
>>> changes bundled into one patch here:
>>>
>>> 1. Changing bd->props.state and bd->props.fb_blank only when use_count
>>>    changes from 0->1 or 1->0.
>>>
>>> 2. Calling backlight_update_status() only with the above change, and not
>>>    on all notifier callbacks.
>>>
>>> 3. Setting bd->props.fb_blank always to either FB_BLANK_UNBLANK or
>>>    FB_BLANK_POWERDOWN instead of *(int *)evdata->data.
> 
> Since I have already post v3(https://lkml.org/lkml/2014/1/22/126) to change the setting for bd->props.fb_blank, the idea of the 3rd point is not very appropriate any more.
> 
>>>
>>> The rationale in the commit message seems plausible, and AFAICT the code
>>> does what it says on the box, so for that (and for that alone) you can
>>> have my
>>>
>>> Reviewed-by: Jani Nikula <jani.nikula@intel.com>
>>>
>>> *BUT* it would be laborous to figure out whether this change in
>>> behaviour might regress some drivers. I'm just punting on that. And that
>>> brings us back to the three changes above - in a bisect POV it might be
>>> helpful to split the patch up. Up to the maintainers.
>>
>> I agree with Jani Nikula's opinion.
>> Please split this patch into three patches as above mentioned.
>>
> 
> I am open to split the patch up.
> However, IMHO, this patch is somewhat self-contained.
> For example, if we try to create 2 patches for the 1st point and the 2nd point Jani mentioned, one patch would invent the use_count and call backlight_update_status() on all notifier callbacks(just
> ignore the use_count).
> Do you think this is a good patch?
> 
> It also doesn't look straightforward for me to create 2 patches for the 1st point and the 3rd point.
                                                                                            ^ Sorry, fix typo(2nd -> 3rd).

> 
> Please advice.
>