Re: [PATCH 1/3] swiotlb: Export maximum allocation size

[Michael S. Tsirkin]

On Mon, Jan 14, 2019 at 03:49:07PM -0500, Konrad Rzeszutek Wilk wrote:
> On Fri, Jan 11, 2019 at 10:12:31AM +0100, Joerg Roedel wrote:
> > On Thu, Jan 10, 2019 at 12:02:05PM -0500, Konrad Rzeszutek Wilk wrote:
> > > Why not use swiotlb_nr_tbl ? That is how drivers/gpu/drm use to figure if they
> > > need to limit the size of pages.
> > 
> > That function just exports the overall size of the swiotlb aperture, no?
> > What I need here is the maximum size for a single mapping.
> 
> Yes. The other drivers just assumed that if there is SWIOTLB they would use
> the smaller size by default (as in they knew the limitation).
> 
> But I agree it would be better to have something smarter - and also convert the
> DRM drivers to piggy back on this.
> 
> Or alternatively we could make SWIOTLB handle bigger sizes..


Just a thought: is it a good idea to teach blk_queue_max_segment_size
to get the dma size? This will help us find other devices
possibly missing this check.


> > 
> > Regards,
> > 
> > 	Joerg