On Tue, Sep 01, 2020 at 05:40:49PM +0200, Christoph Hellwig wrote: > On Tue, Sep 01, 2020 at 05:36:17PM +0200, Ulf Hansson wrote: > > > I still don't think this makes sense, as the dma_mask should always > > > be non-NULL here. > > > > If that is the case, I wonder how the driver could even have worked without DMA. > > > > Because in the existing code, host->dma_dev gets assigned to > > spi->master->dev.parent->dma_mask - which seems to turn on the DMA > > usage in the driver. > > > > What am I missing? > > Do you know of other non-DMA users? For SH nommu it probably worked > because SH nommu used to provide a DMA implementation that worked > fine for streaming maps, but was completely broken for coherent > allocation. And this driver appears to only use the former. On the system we're using it on, there's no DMA whatsoever. It just used to allow memory allocations suitable for DMA (which any allocation vacuuously is when there's no DMA) but now it doesn't, due to your change. Just below the if block in question in this thread is: host->readback.is_dma_mapped = (host->dma_dev != NULL); and similar conditions appear elsewhere all over the file in the form of if (host->dma_dev). Of course doing DMA requires a link to a DMA controller device, and plenty SPI devices (most obviously bit-banged ones) lack DMA. The right condition for the block in question here is probably just checking dma_dev instead of dma_mask or CONFIG_HAS_DMA, but it seems useful to optimize out the code if CONFIG_HAS_DMA is false, anyway. Rich
