tinydrm: page allocation failure

[David Lechner]

On 12/11/2017 07:37 AM, Noralf Trønnes wrote:
> 
> Den 11.12.2017 13.45, skrev Noralf Trønnes:
>>
>> 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?
>>>
>>
>> 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.
>>
> 
> tinydrm has a spi_max module parameter that can set the chunk size.
> I have wondered if I should just remove this parameter when spi-bcm2835
> has been fixed as explained here:
> https://lists.freedesktop.org/archives/dri-devel/2017-February/132725.html
> I'm figuring it is better to add this parameter if the problem arises 
> again,
> instead of preparing for something that might not be a problem anymore.
> 
> But now I'm reminded of this dummy buffer and if we were to send the entire
> framebuffer in one go, the dummy buffer would have to be the same size as
> the framebuffer. Not sure how well that works on long running boards with
> little ram, to be able to allocate 320*480*2 = 300kB ~= 512kB (continous)
> for the largest SPI displays on every flush, after months of run time.
> 
> How much ram do you have on the Lego module?

64MB