[Bug 204145] amdgpu video playback causes host to hard reset (checkstop) on POWER9 with RX 580

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=204145

--- Comment #16 from Shawn Anastasio (shawn at anastas.io) ---
Created attachment 283799
  --> https://bugzilla.kernel.org/attachment.cgi?id=283799&action=edit
test patch #1

Though I'm not familiar with this code, a quick spot check shows what I believe 
to be an inconsistency with the commit's claim of functional identicality. 
Namely, the previous caller of __dma_get_coherent_pfn (now 
arch_dma_coherent_to_pfn) would explicitly modify the vm_area to mark it as 
uncacheable in the !coherent case. It seems the new caller (dma_common_mmap)
does not do this. I have written a small patch to restore the previous 
behavior (I think). Note that this probably isn't upstreamable since this fix 
should probably go somewhere in the powerpc arch code rather than the dma core.

Tim, since you're the only one who can easily reproduce this,
would you mind giving this patch a shot?

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