On 07/27/2018 05:55 AM, Robin Murphy wrote:

Hi Grygorii,

Thanks for the report.

On 27/07/18 00:45, Grygorii Strashko wrote:
[...]

quoted

With this series applied I can't boot TI ARM32 am574x-idk any more.

And log output is full of "DMA mask not set" -

That's somewhat expected - as the relevant commit message mentions, 
there will be bugs flushed out by this change, but the point is to fix 
them :)

quoted

nobody sets dma_mask for platform bus in case of OF boot :(

Right, after a brief investigation, that one turns out to be nice and 
straightforward to explain and fix; I'll write up the patch shortly.

[...]

quoted

[??? 3.793493] ti-qspi 4b300000.qspi: dma_alloc_coherent failed, using 
PIO mode
[??? 3.801088] Unable to handle kernel NULL pointer dereference at 
virtual address 00000080

[...]

quoted

[??? 4.602777] [<c04d87a4>] (omap_dma_write) from [<c04d8dc0>] 
(omap_dma_start_desc+0x78/0x150)
[??? 4.611258] [<c04d8d48>] (omap_dma_start_desc) from [<c04d9028>] 
(omap_dma_issue_pending+0x90/0x98)
[??? 4.620347]? r9:ed002780 r8:00000000 r7:00000010 r6:ee2bdd00 
r5:ee2bdd4c r4:ee2bdd00
[??? 4.628130] [<c04d8f98>] (omap_dma_issue_pending) from [<c0608d1c>] 
(ti_qspi_dma_xfer+0x8c/0x13c)
[??? 4.637039]? r5:00000000 r4:ee7e1b28
[??? 4.640636] [<c0608c90>] (ti_qspi_dma_xfer) from [<c06090b0>] 
(ti_qspi_exec_mem_op+0x2e4/0x32c)

Hooray, a real bug! Since dma_alloc_coherent() could have failed due to 
lack of memory or any other reason, that's not even directly related to 
this change, we've simply helped uncover it. I guess that PIO fallback 
path hasn't been tested recently, because it clearly doesn't work. It 
would be good if someone who knows the ti-qspi driver and has the means 
to test it could figure that one out before also adding the missing 
dma_set_coherent_mask() call.

yes. ti-qspi has an issues with PIO mode. 

But, reason of failure is this warning:

[    3.482502] WARNING: CPU: 0 PID: 1 at ./include/linux/dma-mapping.h:516 ti_qspi_probe+0x4a4/0x50c

which is caused by this series - which makes coherent_dma_mask constantly 0 by default,
so dma_alloc_coherent() - fails.

Robin.

-- 
regards,
-grygorii