Re: [PATCH v1 0/2] dma: fix dma_opt_mapping_size() returning bogus value when no backend hint exists

[John Garry]

On 17/03/2026 14:36, Christoph Hellwig wrote:
> On Tue, Mar 17, 2026 at 09:11:59AM +0000, John Garry wrote:
> > For SAS controllers, don't we limit shost->opt_sectors at
> > shost->max_sectors, and then in sd_revalidate_disk() this value is ignored
> > as sdkp->opt_xfer_blocks would be smaller, right?
> That assumes opt_xfer_blocks is actually set.  It's an optional and
> relatively recent SCSI feature.  So don't expect crappy SSDs or
> RAID controllers faking up SCSI in shitty firmware to actually set
> it.

Sure, and then we would have io_opt at max_sectors, and it seems that 
value is totally configurable for that HBA driver.

However I still find the values reported strange:
swidth=4095 / sunit=2

I thought that they were from io_opt and io_min, and 
blk_validate_limits() does rounding to PBS, except io_min has no 
rounding for > PBS.