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

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Date:   Wed, 16 Jan 2019 06:37:26 +0000
From:   Oleksandr Andrushchenko <Oleksandr_Andrushchenko@...m.com>
To:     Gerd Hoffmann <kraxel@...hat.com>,
        Oleksandr Andrushchenko <andr2000@...il.com>
CC:     "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "daniel.vetter@...el.com" <daniel.vetter@...el.com>,
        "jgross@...e.com" <jgross@...e.com>,
        "boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
        "noralf@...nnes.org" <noralf@...nnes.org>,
        "hch@...radead.org" <hch@...radead.org>
Subject: Re: [PATCH v2] drm/xen-front: Make shmem backed display buffer
 coherent

On 1/16/19 8:30 AM, 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?
My bad, will add the comment
> cheers,
>    Gerd
>
Thank you,
Oleksandr