Den 15.10.2019 17.59, skrev Andy Shevchenko: > 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? > Please do. I still believe that this papers over a controller driver bug/shortcoming, but there could be more drivers that have the same problem so it's better to revert to the old behaviour. I guess the problem is that not many controller drivers are tested with buffers bigger than max_dma_len (64kB in this case, same as for the Pi). If I have the revert by tomorrow, then I can apply it before Maxime sends the -rc PR to Dave on Thursday. Noralf. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
