Re: [PATCH v7 1/1] scsi: sas: skip opt_sectors when DMA reports no real optimization hint

[John Garry]

On 24/04/2026 14:21, Christoph Hellwig wrote:

Responding to get things moving..

> > + */
> > +static void sas_dma_setup_opt_sectors(struct Scsi_Host *shost)
> > +{
> > +	struct device *dma_dev = shost->dma_dev;
> > +	size_t opt, max;
> > +	unsigned int opt_sectors;
> > +
> > +	if (!dma_dev->dma_mask)
> > +		return;
> Upper layers have no real busines looking at dma_dev->dma_mask. What
> is this check intended to do?

Back when that check was introduced, dma_max_mapping_size() may crash 
for some SCSI hosts. See 
https://lore.kernel.org/linux-scsi/BYAPR04MB58168CBFF8B691DF33C73DDBE7C40@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

scsi_debug would be an example of such a shost as it is not DMA capable. 
That crash is not an issue any longer from my limited testing. I think 
that it comes down to new checks in dma_addressing_limited() -> 
__dma_addressing_limited() for dma_mask being set. So we may be able to 
get rid of that dma_mask check.