On Wed, Aug 30, 2023 at 12:04 AM Christoph Hellwig <hch@xxxxxx> wrote: > > On Tue, Aug 29, 2023 at 12:14:44PM +0100, Robin Murphy wrote: > > dma_get_max_seg_size() represents a capability of the device itself, namely > > the largest contiguous range it can be programmed to access in a single DMA > > descriptor/register/whatever. > > Yes. In a way it's a bit odd that it ended up in a field in > struct device, as the feature might actually be different for different > DMA engines or features in a device. If I was to redesign it from > scratch I'd just pass it to dma_map_sg. > > >> Generally looking at videobuf2-dma-sg, I feel like we would benefit > >> from some kind of dma_alloc_table_from_pages() that simply takes the > >> struct dev pointer and does everything necessary. > > > > Possibly; this code already looks lifted from drm_prime_pages_to_sg(), and > > if it's needed here then presumably vb2_dma_sg_get_userptr() also needs it, > > at the very least. > > Yes, there's tons of them. But I'd feel really bad adding even more > struct scatterlist based APIs given how bad of a data structure that is. Do we see anything replacing it widely anywhere on the short-middle term horizon? I think we could possibly migrate vb2 to use that new thing internally and just provide some compatibility X to scatterlist conversion function for the drivers.
