Re: [PATCH v4.19.y, v4.14.y, v4.9.y] drm/etnaviv: Backport fix for mmu flushing

[Greg KH]

On Thu, Apr 02, 2020 at 06:07:55PM +0100, Robert Beckett wrote:
> commit 4900dda90af2cb13bc1d4c12ce94b98acc8fe64e upstream
> 
> Due to async need_flush updating via other buffer mapping, checking
> gpu->need_flush in 3 places within etnaviv_buffer_queue can cause GPU
> hangs.
> 
> This occurs due to need_flush being false for the first 2 checks in that
> function, so that the extra dword does not get accounted for, but by the
> time we come to check for the third time, gpu->mmu->need_flish is true,
> which outputs the flush instruction. This causes the prefetch during the
> final link to be off by 1. This causes GPU hangs.
> 
> It causes the ring to contain patterns like this:
> 
> 0x40000005, /* LINK (8) PREFETCH=0x5,OP=LINK */                                                      
> 0x70040010, /*   ADDRESS *0x70040010 */                                                              
> 0x40000002, /* LINK (8) PREFETCH=0x2,OP=LINK */                                                      
> 0x70040000, /*   ADDRESS *0x70040000 */                                                              
> 0x08010e04, /* LOAD_STATE (1) Base: 0x03810 Size: 1 Fixp: 0 */                                       
> 0x0000001f, /*   GL.FLUSH_MMU := FLUSH_FEMMU=1,FLUSH_UNK1=1,FLUSH_UNK2=1,FLUSH_PEMMU=1,FLUSH_UNK4=1 */
> 0x08010e03, /* LOAD_STATE (1) Base: 0x0380C Size: 1 Fixp: 0 */                                       
> 0x00000000, /*   GL.FLUSH_CACHE := DEPTH=0,COLOR=0,TEXTURE=0,PE2D=0,TEXTUREVS=0,SHADER_L1=0,SHADER_L2=0,UNK10=0,UNK11=0,DESCRIPTOR_UNK12=0,DESCRIPTOR_UNK13=0 */
> 0x08010e02, /* LOAD_STATE (1) Base: 0x03808 Size: 1 Fixp: 0 */                                       
> 0x00000701, /*   GL.SEMAPHORE_TOKEN := FROM=FE,TO=PE,UNK28=0x0 */                                    
> 0x48000000, /* STALL (9) OP=STALL */                                                                 
> 0x00000701, /*   TOKEN FROM=FE,TO=PE,UNK28=0x0 */                                                    
> 0x08010e00, /* LOAD_STATE (1) Base: 0x03800 Size: 1 Fixp: 0 */                                       
> 0x00000000, /*   GL.PIPE_SELECT := PIPE=PIPE_3D */                                                   
> 0x40000035, /* LINK (8) PREFETCH=0x35,OP=LINK */                                                     
> 0x70041000, /*   ADDRESS *0x70041000 */
> 
> Here we see a link with prefetch of 5 dwords starting with the 3rd
> instruction. It only loads the 5 dwords up and including the final
> LOAD_STATE. It needs to include the final LINK instruction.
> 
> This was seen on imx6q, and the fix is confirmed to stop the GPU hangs.
> 
> The commit referenced inadvertently fixed this issue by checking
> gpu->mmu->need_flush once at the start of the function.
> Given that this commit is independant, and useful for all version, it
> seems sensible to backport it to the stable branches.
> 
> 

All now queued up, thanks for the backports.

greg k-h