[PATCH v2 05/11] drm/tinydrm: Remove tinydrm_spi_max_transfer_size()

[Noralf Trønnes]

Den 15.10.2019 16.32, skrev Andy Shevchenko:
> On Fri, Jul 19, 2019 at 05:59:10PM +0200, Noralf Trønnes wrote:
>> spi-bcm2835 can handle >64kB buffers now so there is no need to check
>> ->max_dma_len. The tinydrm_spi_max_transfer_size() max_len argument is
>> not used by any callers, so not needed.
>>
>> Then we have the spi_max module parameter. It was added because
>> staging/fbtft has support for it and there was a report that someone used
>> it to set a small buffer size to avoid popping on a USB soundcard on a
>> Raspberry Pi. In hindsight it shouldn't have been added, I should have
>> waited for it to become a problem first. I don't know it anyone is
>> actually using it, but since tinydrm_spi_transfer() is being moved to
>> mipi-dbi, I'm taking the opportunity to remove it. I'll add it back to
>> mipi-dbi if someone complains.
>>
>> With that out of the way, spi_max_transfer_size() can be used instead.
>>
>> The chosen 16kB buffer size for Type C Option 1 (9-bit) interface is
>> somewhat arbitrary, but a bigger buffer will have a miniscule impact on
>> transfer speed, so it's probably fine.
> 
> This breaks the SPI PXA2xx case I'm using. The world is not a Pi:e.
> 
> [  388.445752] mi0283qt spi-PRP0001:01: DMA disabled for transfer length 153600 greater than 65536
> [  388.634437] mi0283qt spi-PRP0001:01: DMA disabled for transfer length 153600 greater than 65536
> [  388.822933] mi0283qt spi-PRP0001:01: DMA disabled for transfer length 153600 greater than 65536
> 
> The crucial thing is to check the transfer size against maximum DMA length
> of the master.
> 

Isn't this a spi controller driver problem?
spi_max_transfer_size() tells the client what the maximum transfer
length is. The controller driver can use ctlr->max_transfer_size if it
has restrictions.
AFAIUI max_dma_len is used when splitting up the buffer for the sg table
in spi_map_buf().

Noralf.

> Please, fix.
>