Hi Jingoo,

On Monday, October 24, 2016, Lukasz Majewski wrote:

quoted

Hi Jingoo,

quoted

On Saturday, October 22, 2016, Lukasz Majewski wrote:

quoted

The commit: a55944ca82d287ca099ca90413af857af9086773 has posed
some extra

Please add the 'subject' of patch as below.

The commit a55944ca82d2 ("backlight: update bd state & fb_blank
properties when necessary ") has posted some extra.

Ok, I will add such information.

However, I'm more interested in some technical comments regarding
proposed fix.

Could you provide some feedback on the technical side of the patch?

Best regards,
Łukasz Majewski

Best regards,
Jingoo Han

quoted

quoted

Please add the subject of the patch, in order to let people know
which patch you mention exactly. Please loot at other commits that
fixed bugs or behavior
of other patches.

Thanks for the tip.

The mentioned patch:

commit a55944ca82d287ca099ca90413af857af9086773
Author: Liu Ying [off-list ref]
Date:   Thu Apr 3 14:48:54 2014 -0700

    backlight: update bd state & fb_blank properties when necessary

    We don't have to update the state and fb_blank properties of a
backlight
    device every time a blanking or unblanking event comes because
they may
    have already been what we want.  Another thought is that one
backlight device may be shared by multiple framebuffers.  The
backlight driver should take the backlight device as a resource
shared by all the associated framebuffers.

    This patch adds some logic to record each framebuffer's
backlight usage
    to determine the backlight device use count and whether the two
    properties should be updated or not.  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 an unblanked framebuffer or
blank a blanked framebuffer.


Could you provide more feedback regarding provided fix?

Thanks in advance,

Łukasz Majewski

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restrictions on blanking and unblanking frame buffer device.

Unfortunately, pwm_bl driver's probe did not initialize members
of struct backlight_device necessary for further blank/unblank
operation.

This code in case of initial unblank of backlight device
(default behaviour) sets use_count to 1 and marks this
particular backlight device as used by all available fb devices
(since it is not known during probe how much and which fb
devices will be assigned).

Without this code, the backlight works properly until one tries
to blank it manually from sysfs with "echo 1

quoted

/sys/class/graphics/fb0/blank". Since fb_bl_on[0] and
use_count were both set to 0, the logic at

fb_notifier_callback (@backlight.c) thought that we didn't turn
on (unblanked) the backlight device and refuses to disable
(blank) it. As a result we see garbage from fb displayed.


Signed-off-by: Lukasz Majewski <redacted>
---
The patch has been tested on i.MX6q with vanilla 4.7 and 4.8
kernels. It applies on 4.9-rcX SHA1:
dcd4693cf47801b7d988ea897519de90dfd25d17.

---
 drivers/video/backlight/pwm_bl.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/video/backlight/pwm_bl.c

b/drivers/video/backlight/pwm_bl.c
index 8040fd6..def39e8 100644

--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c

@@ -203,7 +203,7 @@ static int pwm_backlight_probe(struct

platform_device *pdev)
 	struct pwm_bl_data *pb;
 	int initial_blank = FB_BLANK_UNBLANK;
 	struct pwm_args pargs;
-	int ret;
+	int ret, i;

 	if (!data) {
 		ret = pwm_backlight_parse_dt(&pdev->dev,
&defdata); @@ - 349,6 +349,14 @@ static int
pwm_backlight_probe(struct platform_device *pdev)

 	bl->props.brightness = data->dft_brightness;
 	bl->props.power = initial_blank;
+
+	if (initial_blank == FB_BLANK_UNBLANK) {
+		for (i = 0; i < FB_MAX; i++)
+			bl->fb_bl_on[i] = true;
+
+		bl->use_count = 1;
+	}
+
 	backlight_update_status(bl);

 	platform_set_drvdata(pdev, bl);
--
2.1.4