linux-kernel - Re: [PATCH v2] drm/xen-front: Make shmem backed display buffer coherent

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Message-ID: <20190116063002.jq3aas6ofhaogmyk@sirius.home.kraxel.org>
Date:   Wed, 16 Jan 2019 07:30:02 +0100
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Oleksandr Andrushchenko <andr2000@...il.com>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, daniel.vetter@...el.com,
        jgross@...e.com, boris.ostrovsky@...cle.com, noralf@...nnes.org,
        hch@...radead.org,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: Re: [PATCH v2] drm/xen-front: Make shmem backed display buffer
 coherent

  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?

cheers,
  Gerd