tinydrm: page allocation failure

[David Lechner]

On 12/11/2017 06:45 AM, Noralf Trønnes wrote:
> 
> Den 11.12.2017 04.28, skrev David Lechner:
>> I'm using drm-misc/drm-misc-next and occasionally getting errors as 
>> seen in the stack traces below. I'm not really sure what to make of 
>> it. Any ideas?
>>

I'm starting to wonder if there is some sort of race condition involved. 
I only get this warning on some boots, but when I do, it happens 
multiple times. Also, when I was debugging a an unrelated problem, I 
enabled some of the spin lock checking kernel options that really slow 
down the kernel. When I did this, I got this warning all of the time.

Would it be sensible to allocate a dummy RX buffer once instead of 
letting SPI allocate a new one for every transfer?

> 
> The spi controller driver has told the spi core to allocate dummy
> buffers for tx/rx: spi_sync -> __spi_pump_messages -> spi_map_msg
> -> krealloc -> __do_krealloc -> kmalloc_track_caller
> 
> order:4 means it's trying to allocate 2^4*PAGE_SIZE = 64kB, which
> probably is the max DMA limit. So this is a pixel data transfer.
> 
> On my Raspberry Pi I've got 43 chunks of 64kB available if I have
> understood this right:
> 
> $ sudo cat /proc/buddyinfo
> Node 0, zone   Normal     40     68     66     51     43     46 13 
> 1      3      3     75
> 
> I don't know what those dummy buffers are used for.
> 
> Noralf.
>