RE: How to resolve an issue in swiotlb environment?

[Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>]

Hi Christoph,

> From: Christoph Hellwig, Sent: Wednesday, June 12, 2019 4:31 PM
> 
> First things first:
> 
> Yoshihiro, can you try this git branch?  The new bits are just the three
> patches at the end, but they sit on top of a few patches already sent
> out to the list, so a branch is probably either:
> 
>    git://git.infradead.org/users/hch/misc.git scsi-virt-boundary-fixes

Thank you for the patches!
Unfortunately, the three patches could not resolve this issue.
However, it's a hint to me, and then I found the root cause:
 - slave_configure() in drivers/usb/storage/scsiglue.c calls
   blk_queue_max_hw_sectors() with 2048 sectors (1 MiB) when USB_SPEED_SUPER or more.
 -- So that, even if your patches (also I fixed it a little [1]) could not resolve
    the issue because the max_sectors is overwritten by above code.

So, I think we should fix the slave_configure() by using dma_max_mapping_size().
What do you think? If so, I can make such a patch.

[1]
In the "scsi: take the DMA max mapping size into account" patch,
+       shost->max_sectors = min_t(unsigned int, shost->max_sectors,
+                       dma_max_mapping_size(dev) << SECTOR_SHIFT);

it should be:
+                       dma_max_mapping_size(dev) >> SECTOR_SHIFT);

But, if we fix the slave_configure(), we don't need this patch, IIUC.

Best regards,
Yoshihiro Shimoda

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