On Tue 2018-05-22 22:41:39, Aaro Koskinen wrote: > Hi, > > On Tue, May 22, 2018 at 10:02:50AM +0200, Pali Rohár wrote: > > Hi! I remember that in time of migration from platform board code to > > device tree structures there appeared some bug which caused that > > sometimes display were not initialized. And somebody figured out that > > display initialization is failing when some other SPI devices are > > initialized before or after display... This behavior was observed only > > on real N900 hardware, not in qemu. > > Touchscreen needs to be initialized before display. This is documented > in the DTS, see arch/arm/boot/dts/omap3-n900.dts: > > * For some reason, touchscreen is necessary for screen to work at > * all on real hw. It works well without it on emulator. > * > * Also... order in the device tree actually matters here. > > > Real reason was never explained. In old platform board code there was > > hardcoded order of SPI devices in which initialization happened. And in > > device tree it is probably in (pseudo)-random order. Enabling/disabling > > various config option can affect some timings and order in which kernel > > starts probing and initializing devices... > > The issue was also somewhat present with platform/board code, see e.g. > commit e65f131a14726e5f1b880a528271a52428e5b3a5. > > My device worked with v4.17-rc1 (haven't found time to test newer kernels), > but if you say the probe order is random then we must find some proper way > to express the dependency. I started bisect, but.. that will probably not be useful. If your device works ok in v4.17-rc1, it probably works in newer -rcs, too. Thanks for the ordering hint, I'll try to figure out what is going on there. Pavel # bad: [60cc43fc888428bb2f18f08997432d426a243338] Linux 4.17-rc1 # good: [0adb32858b0bddf4ada5f364a84ed60b196dbcda] Linux 4.16 git bisect start 'v4.17-rc1' 'v4.16' # bad: [ac9053d2dcb9e8c3fa35ce458dfca8fddc141680] Merge tag 'usb-4.17-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb git bisect bad ac9053d2dcb9e8c3fa35ce458dfca8fddc141680 # bad: [bb2407a7219760926760f0448fddf00d625e5aec] Merge tag 'docs-4.17' of git://git.lwn.net/linux git bisect bad bb2407a7219760926760f0448fddf00d625e5aec # bad: [1c7095d2836baafd84e596dd34ba1a1293a4faa9] Merge airlied/drm-next into drm-misc-next git bisect bad 1c7095d2836baafd84e596dd34ba1a1293a4faa9 -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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