potential regression in drm/mgag200

[Thomas Zimmermann]

Hi

Am 04.09.19 um 08:49 schrieb Davidlohr Bueso:
> Hi,
> 
> While doing some changes to x86's pat code and thus having 'debugpat', I
> noticed
> some weird behavior in a server running linux-next as of -- yes,
> reverting does 'fix'
> the issue:
> 
> 90f479ae51a (drm/mgag200: Replace struct mga_fbdev with generic
> framebuffer emulation)
> 
> Where the following splat is seen over and over endlessly for the same
> range:
> 
> x86/PAT: Overlap at 0xd0000000-0xd1000000
> x86/PAT: reserve_memtype added [mem 0xd0000000-0xd02fffff], track
> write-combining, req write-combining, ret write-combining
> x86/PAT: free_memtype request [mem 0xd0000000-0xd02fffff]
> 
> And all these are doing ioremap from drm_fb_helper_dirty_work():
> 
> [  114.330825]  reserve_memtype+0x1b0/0x410
> [  114.330829]  ? ttm_bo_kmap+0x1d7/0x270 [ttm]
> [  114.330830]  __ioremap_caller.constprop.14+0xf6/0x300
> [  114.330832]  ? soft_cursor+0x1f9/0x220
> [  114.330835]  ttm_bo_kmap+0x1d7/0x270 [ttm]
> [  114.330838]  ? ttm_bo_del_sub_from_lru+0x29/0x40 [ttm]
> [  114.330841]  drm_gem_vram_kmap+0x54/0x70 [drm_vram_helper]
> [  114.330842]  drm_gem_vram_object_vmap+0x23/0x40 [drm_vram_helper]
> [  114.330853]  drm_gem_vmap+0x1f/0x60 [drm]
> [  114.477697]  drm_client_buffer_vmap+0x1d/0x30 [drm]
> [  114.477703]  drm_fb_helper_dirty_work+0x92/0x180 [drm_kms_helper]
> [  114.477706]  process_one_work+0x1f4/0x3e0
> [  114.477707]  worker_thread+0x2d/0x3e0
> 
> Before, the same range was also added, but only once, and fwiw it was
> the same either
> with 24 or 32 bpp.
> 
> Any thoughts?

Thanks for reporting. The original code kept around memory mappings for
a longer time, while the new code remapped frequently. I've just
submitted a patch set that restores the old behavior. [1] Fixes the
problem on my test machine.

Best regards
Thomas

[1] https://patchwork.freedesktop.org/series/66210/

> 
> Thanks,
> Davidlohr

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah
HRB 21284 (AG Nürnberg)

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