On Tue, Oct 15, 2019 at 05:41:53PM +0200, Noralf Trønnes wrote:
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?
It doesn't matter. This patch made a regression. Before it worked, now it doesn't.
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.
It might be a problem of the SPI core.
AFAIUI max_dma_len is used when splitting up the buffer for the sg table in spi_map_buf().
Please, fix.
Should I send the revert?