Dear Maintainer, I investigated a bit more this issue and upon further reading these sources regarding similar hardware: - Backlight init fails on Surface 3 if module load order is wrong [1] - Linux on the Dell Venue 8 Pro [2]
I gave a try at recompiling the linux kernel 5.8 from buster backports with these two main changes (full diff below): > $ diff /boot/config-5.8.0-0.bpo.2-amd64 config-t100ta > # [...] > < CONFIG_I2C_DESIGNWARE_PCI=m > --- > > CONFIG_I2C_DESIGNWARE_PCI=y > 8327c8327 > < # CONFIG_PWM_CRC is not set > --- > > CONFIG_PWM_CRC=y > # [...] The resulting kernel allows indeed to adjust the screen backlight and to completely turn it off, even though the following error message still appears: > asus kernel: i915 0000:00:02.0: [drm] *ERROR* Failed to own gpio for > panel control Now the T100TA manages to go to suspend with the screen being completely turned off, when otherwise it usually stays turned on and just blank. I am not sure if the device can actually suspend to ram, even with this change only the suspend-to-idle seems available: > $ cat /sys/power/mem_sleep > [s2idle] Nevertheless, battery life is improved with this change. Do you think this configuration can be applied as default? Baytrail chipset based devices would benefit of it. Cheers [1] https://gitlab.freedesktop.org/drm/intel/-/issues/26 [2] https://www.studioteabag.com/science/dell-venue-pro-linux/ Full kernel configuration diff: > diff /boot/config-5.8.0-0.bpo.2-amd64 config-t100ta > 5c5 > < CONFIG_CC_VERSION_TEXT="gcc-8 (Debian 8.3.0-6) 8.3.0" > --- > > CONFIG_CC_VERSION_TEXT="gcc (Debian 8.3.0-6) 8.3.0" > 4134c4134 > < CONFIG_I2C_DESIGNWARE_PCI=m > --- > > CONFIG_I2C_DESIGNWARE_PCI=y > 8327c8327 > < # CONFIG_PWM_CRC is not set > --- > > CONFIG_PWM_CRC=y > 9138c9138 > < CONFIG_SYSTEM_TRUSTED_KEYS="debian/certs/debian-uefi-certs.pem" > --- > > CONFIG_SYSTEM_TRUSTED_KEYS="" > 9296,9302c9296 > < CONFIG_DEBUG_INFO=y > < # CONFIG_DEBUG_INFO_REDUCED is not set > < # CONFIG_DEBUG_INFO_COMPRESSED is not set > < # CONFIG_DEBUG_INFO_SPLIT is not set > < # CONFIG_DEBUG_INFO_DWARF4 is not set > < # CONFIG_DEBUG_INFO_BTF is not set > < # CONFIG_GDB_SCRIPTS is not set > --- > > # CONFIG_DEBUG_INFO is not set
