On 09/28/2015 11:19 AM, Simon Guinot wrote:
On Mon, Sep 28, 2015 at 10:02:35AM +0200, Jacek Anaszewski wrote:
Hi Simon,
Hi Jacek,
Does your device support reading the brightness currently set?
No it don't.
If so, it would be good to implement brightness_get op, because
AFAIR you mentioned that the firmware you are working with sets
always maximum brightness value. Having the op implemented would
allow to find this out.
I don't understand how this can help. I mean, the only issue is that at
startup the initial LED state is unknown. And the software brightness
value could be false. But once the LED is configured, the brightness
values for software and hardware are synchronized. The brightness value
is stored/cached in led_classdev and it can be retrieved by the user via
sysfs...
For my own knowledge, is there some interest in having brightness_get(),
aside of guessing the LED initial state ?
Some LED controllers can adjust brightness in case battery voltage level
falls below some threshold.
What does the embedded firmware is writing 255 or 0 into the brightness
sysfs attribute. The max_brightness value is ignored. After this patch,
writing 255 and 0 still allows to configure the LED in the same way:
maximum brightness or off. Thus, I believe there is no compatibility
issue.
LED core always assures that brightness value passed to brightness_set
op does not exceed max_brightness value. So, now after executing
"echo 255 > brightness", LED core will adjust it to max_brightness
(e.g. 7) before passing to brightness_set.
In the message [1], you mentioned that "LEDs are only enabled at their
maximum level", so IIUC following is possible:
#echo 3 > "brightness"
firmware sets brightness to max_brightness from DT (e.g. 7), but
#cat brightness
#3
Is it true?
But of course, I will update the firmware as well :)
[1] http://www.spinics.net/lists/devicetree/msg94358.html
--
Best Regards,
Jacek Anaszewski
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
