Hi Alex,
On 08/04/16 05:47, Alexandre Courbot wrote:
Hi Robin,
On 04/07/2016 08:50 PM, Robin Murphy wrote:
Hello,
With 4.6-rc2 (and -rc1) I'm seeing Nouveau blowing up at boot, from the
look of it by dereferencing some offset from NULL inside
nouveau_fbcon_imageblit(). My setup is an old XFX 7600GT card plugged
into an ARM Juno r1 board, which works fine with 4.5 and earlier.
Attached are a couple of logs from booting arm64 defconfig plus DRM and
Nouveau enabled - the second also has framebuffer console rotation
turned on, which interestingly seems to move the point of failure, and
the display does eventually come up to show the tail end of the panic in
that case.
I might be able to find time for a full bisection next week if isn't
something sufficiently obvious to anyone who knows this driver.
Looking at the log it is not clear to me what could be causing this. I
can boot 4.6-rc2 with a GM206 card without any issue. A bisect would
indeed be useful here.
OK, turns out the lure of writing something to remotely drive a Juno and
parse kernel bootlogs through an automatic bisection was too great to
resist on a Friday afternoon :D
Bisection came down to 1733a2ad3674("drm/nouveau/device/pci: set as
non-CPU-coherent on ARM64"), and sure enough reverting that removes the
crash. I have to say, that commit looks pretty bogus anyway - since
de335bb49269("PCI: Update DMA configuration from DT") in 4.1, PCI
devices should correctly inherit the coherency property from their host
controller's DT node and get the appropriate DMA ops assigned. From a
brief look at the Nouveau code, I guess it could possibly be the
assumptions the TTM stuff going awry in the presence of coherent DMA
ops. Regardless of how the code goes wrong, though, it's trivially
incorrect to have a blanket statement that PCI devices are non-coherent
on arm64, so whatever the original issue was this isn't the right way to
fix it.
Robin.
Thanks,
Alex.
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