On Thu, Apr 11, 2019 at 11:00:56AM +0200, Ulf Hansson wrote: > > blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, mq->queue); > > if (mmc_can_erase(card)) > > mmc_queue_setup_discard(mq->queue, card); > > > > - blk_queue_bounce_limit(mq->queue, limit); > > + if (!mmc_dev(host)->dma_mask || !*mmc_dev(host)->dma_mask) > > + blk_queue_bounce_limit(mq->queue, BLK_BOUNCE_HIGH); > > So this means we are not going to set a bounce limit for the queue, in > case we have a dma mask. > > Why isn't that needed no more? Whats has changed? On most architectures it was never needed, the major hold out was x86-32 with PAE. In general the dma_mask tells the DMA API layer what is supported, and if the physical addressing doesn't support that it has to use bounce buffering like swiotlb (or dmabounce on arm32). A couple month ago I finally fixes x86-32 to also properly set up swiotlb, and remove the block layerer bounce buffering that wasn't for highmem (which is about having a kernel mapping, not addressing), and ISA DMA (which is not handled like everything else, but we'll get there). But for some reason I missed mmc back then, so mmc right now is the only remaining user of address based block layer bouncing.
