From: Christoph Hellwig <hch@infradead.org>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: Oleksandr Andrushchenko <andr2000@gmail.com>,
xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
dri-devel@lists.freedesktop.org, daniel.vetter@intel.com,
jgross@suse.com, boris.ostrovsky@oracle.com, noralf@tronnes.org,
hch@infradead.org,
Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Subject: Re: [PATCH v2] drm/xen-front: Make shmem backed display buffer coherent
Date: Tue, 15 Jan 2019 22:36:31 -0800 [thread overview]
Message-ID: <20190116063631.GA10881@infradead.org> (raw)
In-Reply-To: <20190116063002.jq3aas6ofhaogmyk@sirius.home.kraxel.org>
On Wed, Jan 16, 2019 at 07:30:02AM +0100, Gerd Hoffmann wrote:
> Hi,
>
> > + if (!dma_map_sg(dev->dev, xen_obj->sgt->sgl, xen_obj->sgt->nents,
> > + DMA_BIDIRECTIONAL)) {
> > + ret = -EFAULT;
> > + goto fail_free_sgt;
> > + }
>
> Hmm, so it seems the arm guys could not come up with a suggestion how to
> solve that one in a better way. Ok, lets go with this then.
>
> But didn't we agree that this deserves a comment exmplaining the purpose
> of the dma_map_sg() call is to flush caches and that there is no actual
> DMA happening here?
Using a dma mapping call to flush caches is complete no-go. But the
real question is why you'd even want to flush cashes if you do not
want a dma mapping?
This whole issue keeps getting more and more confusing.
next prev parent reply other threads:[~2019-01-16 6:36 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-15 14:04 [PATCH v2] drm/xen-front: Make shmem backed display buffer coherent Oleksandr Andrushchenko
2019-01-16 6:30 ` Gerd Hoffmann
2019-01-16 6:36 ` Christoph Hellwig [this message]
2019-01-16 6:43 ` Oleksandr Andrushchenko
2019-01-17 9:18 ` Christoph Hellwig
2019-01-18 9:40 ` Oleksandr Andrushchenko
2019-01-18 11:43 ` [Xen-devel] " Julien Grall
2019-01-21 12:43 ` Oleksandr Andrushchenko
2019-01-21 17:09 ` Julien Grall
2019-01-22 10:28 ` Oleksandr Andrushchenko
2019-01-22 11:44 ` Julien Grall
2019-01-24 14:34 ` Oleksandr Andrushchenko
2019-01-24 15:02 ` Julien Grall
2019-01-29 14:46 ` Oleksandr Andrushchenko
2019-01-30 8:39 ` Oleksandr Andrushchenko
2019-01-16 6:37 ` Oleksandr Andrushchenko
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