On Wed, 4 Dec 2019 at 08:14, Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> wrote: > > On Wed, 4 Dec 2019 14:00:08 +0800 Jun Nie wrote: > > > > > > > Christoph Hellwig <hch@xxxxxxxxxxxxx> 于2019年12月3日周二 下午3:36写道： > > > > > > On Tue, Dec 03, 2019 at 11:29:15AM +0800, Jun Nie wrote: > > > > Thanks for the reminder! So I need to parse the segment_boundary from > > > > device tree and use below code to set it, right? > > > > For the max_segments accounting error, I did not see it so far though I > > > > believe it is true in theory. Maybe it is due to segment boundary value is > > > > very large. > > > > > > > > +++ b/drivers/mmc/core/queue.c > > > > @@ -374,6 +374,7 @@ static void mmc_setup_queue(struct mmc_queue *mq, > > > > struct mmc_card *card) > > > > WARN(!blk_queue_can_use_dma_map_merging(mq->queue, > > > > mmc_dev(host)), > > > > "merging was advertised but not possible"); > > > > + blk_queue_segment_boundary(mq->queue, mmc->segment_boundary); > > > > blk_queue_max_segments(mq->queue, mmc_get_max_segments(host)); > > > > > > Yes, I think should do it. Maybe modulo a check if the low-level > > > driver actually sets a segment boundary. > > > > For the block device, such as SD card, it is right solution. But I > > have concern on SDIO case. Maybe we should add workaround together > > with block layer segment boundary restriction. How do you think about > > it? > > Yes, buffers for SDIO are a consern. Especially since those buffers are allocated by SDIO func drivers or even from upper layers, such as the network stacks, for example. I think SDIO func drivers simply need to respect the constraints the host has set via the .segment_boundary, .max_seg_size, .max_segs, etc. We should export SDIO func APIs to make the information available for the SDIO func drivers. > > Another trouble is how to workaround if the sg is constructed by mmc and > no block layer interactions at all. e.g __mmc_blk_ioctl_cmd(), and all > those sgs in mmc_test.c Those should be easier to fix, as the buffer/sg allocation can be fixed internally by mmc core. Just post some patches. :-) I am more worried about SDIO, as those buffers are not that easy to control. Note that, there have been suggestions on adding an SDIO interface where an sg can be passed [1]. Unfurtunate those patches got stuck and didn't make it. Kind regards Uffe [1] https://patchwork.kernel.org/patch/10123143/
