On Thu, Dec 12, 2013 at 11:36:09AM +0000, Damien Lespiau wrote: > On Wed, Dec 11, 2013 at 06:50:10PM -0200, Paulo Zanoni wrote: > > From: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx> > > > > Fixes regression introduced by: > > commit bf51d5e2cda5d36d98e4b46ac7fca9461e512c41 > > Author: Paulo Zanoni <paulo.r.zanoni at intel.com> > > Date: Wed Jul 3 17:12:13 2013 -0300 > > drm/i915: switch disable_power_well default value to 1 > > > > The bug I'm seeing can be reproduced with: > > - Have vgacon configured/enabled > > - Make sure the power well gets disabled, then enabled. You can > > check this by seeing the messages print by hsw_set_power_well > > - Stop your display manager > > - echo 0 > /sys/class/vtconsole/vtcon1/bind > > > > I can easily reproduce this by blacklising snd_hda_intel and booting > > with eDP+HDMI. > > > > If you do this and then look at dmesg, you'll see we're printing > > infinite "Unclaimed register" messages. This is happening because > > we're stuck on an infinite loop inside console_unlock(), which is > > calling many functions from vgacon.c. And the code that's triggering > > the error messages is from vgacon_set_cursor_size(). > > > > After we re-enable the power well, every time we read/write the VGA > > address 0x3d5 we get an "unclaimed register" interrupt (ERR_INT) and > > print error messages. If we write anything to the VGA MSR register (it > > doesn't really matter which value you write to bit 0), any > > reads/writes to 0x3d5 _don't_ trigger the "unclaimed register" errors > > anymore (even if MSR bit 0 is zero). So what happens with the current > > code is that when we unbind i915 and bind vgacon, we call > > console_unlock(). Function console_unlock() is responsible for > > printing any messages that were supposed to be print when the console > > was locked, so it calls the TTY layer, which calls the console layer, > > which calls vgacon to print the messages. At this point, vgacon > > eventually calls vgacon_set_cursor_size(), which touches 0x3d5, which > > triggers unclaimed register interrupts. The problem is that when we > > get these interrupts, we print the error messages, so we add more work > > to console_unlock(), which will try to print it again, and then call > > vgacon again, trigger a new interrupt, which will put more stuff to > > the buffer, and then we'll be stuck at console_unlock() forever. > > > > If you patch intel_uncore.c to not print anything when we detect > > unclaimed registers, we won't get into the console_unlock() infinite > > loop and the driver unbind will work just fine. We will still be > > getting interrupts every time vgacon touches those registers, but we > > will survive. This is a valid experiment, but IMHO it's not the real > > fix: if we don't print any error messages we will still keep getting > > the interrupts, and if we disable ERR_INT we won't get the interrupt > > anymore, but we will also stop getting all the other error interrupts. > > > > I talked about this problem with the HW engineer and his > > recommendation is "So don't do any VGA I/O or memory access while the > > power well is disabled, and make to re-program MSR after enabling the > > power well and before using VGA I/O or memory accesses.". > > > > Notice that this is just a partial fix to fd.o #67813. This fixes the > > case where the power well is already enabled when we unbind, not when > > it's disabled when we unbind. > > > > V2: - Rebase (first version was sent in September). > > V3: - Complete rewrite of the same fix: smaller implementation, > > improved commit message. > > > > Testcase: igt/drv_module_reload > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=67813 > > Signed-off-by: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx> > > The commit message is convincing! > > Reviewed-by: Damien Lespiau <damien.lespiau@xxxxxxxxx> All three merged, thanks for review&patches. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
