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

[Jisheng Zhang <Jisheng.Zhang@synaptics.com>]

On Wed, 4 Dec 2019 14:00:08 +0800 Jun Nie wrote:

> 
> 
> Christoph Hellwig <hch@infradead.org> 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?
> 

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

Thanks