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

On Thursday, January 23, 2014 6:28 PM, Liu Ying wrote:

On 01/23/2014 01:44 PM, Jingoo Han wrote:

quoted

On Wednesday, January 22, 2014 6:36 PM, Jani Nikula wrote:

quoted

On Mon, 20 Jan 2014, Liu Ying [off-list ref] wrote:

quoted

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 <redacted>
---
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(-)

[.....]

quoted

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.

OK, I see.

quoted

quoted

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 <redacted>

*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?

The calling backlight_update_status() regardless the use_count
Will make the critical side effect? I don't think so.
Also, these two patches will be merged at the same time.
Please, split the patch into two patches. It would be clearer.

One more thing, please keep the indent using "Enter", when
sending your reply mail.

Best regards,
Jingoo Han