<html> <head> <base href="https://bugs.freedesktop.org/"> </head> <body> <div> <a class="bz_bug_link bz_status_REOPENED " title="REOPENED - [BYT LPSS backlight] Acer Aspire Switch 10 backlight control" href="https://bugs.freedesktop.org/show_bug.cgi?id=90075#c17">Comment # 17</a> on <a class="bz_bug_link bz_status_REOPENED " title="REOPENED - [BYT LPSS backlight] Acer Aspire Switch 10 backlight control" href="https://bugs.freedesktop.org/show_bug.cgi?id=90075">bug 90075</a> from <a class="email" href="mailto:miha.frangez@gmail.com" title="Miha Frangež <miha.frangez@gmail.com>"> Miha Frangež</a> <pre>Hi, Shobhit. I've applied your new patches to 4.13.0-rc2 with PWM_LPSS_PLATFORM=y and DRM_I915=m. No PWM chips showed up in /sys/class/pwm. (more details: <a href="https://frangez.tech/switch10/4.13-rc2-switch10-17/">https://frangez.tech/switch10/4.13-rc2-switch10-17/</a>) Then I set PWM_CRC=y and this gave me pwmchip0 in sysfs. It only has one channel, which would make sense for a backlight chip. After exporting that channel however, things stop making sense. Reading /sys/class/pwm/pwmchip0/pwm0/enable shows the channel disabled. Since the screen is at full brightness, this could either mean that it's not used, or that the device has some kind of fallback (so the UEFI team didn't have to mess with PWM in firmware). Writing random values into duty_cycle and period and enabling it succeeded, but didn't do anything (no effect on backlight). (more details: <a href="https://frangez.tech/switch10/4.13-rc2-switch10-17-16/">https://frangez.tech/switch10/4.13-rc2-switch10-17-16/</a>) If there is a CRC PWM chip in there, it's either not used for backlight or the PWM_CRC driver can't control it. Let me know if you need any more info.</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are on the CC list for the bug.</li> <li>You are the assignee for the bug.</li> <li>You are the QA Contact for the bug.</li> </ul> </body> </html>