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

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Message-ID: <20190114204907.GH32038@char.us.oracle.com>
Date:   Mon, 14 Jan 2019 15:49:07 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        virtualization@...ts.linux-foundation.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org, jfehlig@...e.com,
        jon.grimm@....com, brijesh.singh@....com, hch@....de,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 1/3] swiotlb: Export maximum allocation size

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..
> 
> Regards,
> 
> 	Joerg