Re: [PATCH 4/4] mmc: sdhci: Add DMA memory boundary workaround

[Jun Nie <jun.nie@linaro.org>]

Christoph Hellwig <hch@infradead.org> 于2019年12月3日周二 上午1:52写道：
>
> On Mon, Dec 02, 2019 at 10:41:04PM +0800, Jun Nie wrote:
> > DMA memory cannot cross specific boundary for some SDHCI controller,
> > such as DesignWare SDHCI controller. Add DMA memory boundary dt
> > property and workaround the limitation.
>
> If you use blk_queue_segment_boundary to tell the block layer the
> segment boundary restrictions it won't ever send you segments
> that don't fit.  With just the workaround in this patch you'll run into
> max_segments accounting issues, don't you?

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));