From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-6952-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 5F7F3984319 for ; Mon, 16 Mar 2020 10:37:04 +0000 (UTC) From: Dmitry Sepp Date: Mon, 16 Mar 2020 11:36:55 +0100 Message-ID: <2171890.ElGaqSPkdT@os-lin-dmo> In-Reply-To: References: <20200218202753.652093-1-dmitry.sepp@opensynergy.com> <6194402.K2JlShyGXD@os-lin-dmo> MIME-Version: 1.0 Subject: [virtio-dev] Re: [PATCH v2 1/1] video_video: Add the Virtio Video V4L2 driver Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable To: Tomasz Figa Cc: Linux Media Mailing List , Hans Verkuil , virtio-dev@lists.oasis-open.org, Alexandre Courbot , Alex Lau , Daniel Vetter , Dylan Reid , dstaessens@chromium.org, Enrico Granata , Frediano Ziglio , Keiichi Watanabe , Gerd Hoffmann , =?ISO-8859-1?Q?St=E9phane?= Marchesin , Pawel Osciak , spice-devel@lists.freedesktop.org, David Stevens , uril@redhat.com, samiullah.khawaja@opensynergy.com, kiran.pawar@opensynergy.com, Nikolay Martyanov List-ID: Hi Tomasz, On Freitag, 13. M=E4rz 2020 12:11:51 CET Tomasz Figa wrote: > On Fri, Mar 13, 2020 at 11:27 AM Dmitry Sepp >=20 > wrote: > > Hi Tomasz, > >=20 > > On Freitag, 13. M=E4rz 2020 11:05:35 CET Tomasz Figa wrote: > > > On Thu, Mar 12, 2020 at 12:48 PM Dmitry Sepp > > >=20 > > > wrote: > > > > Hi Hans, > > > >=20 > > > > One more thing: > > > > > GFP_DMA? That's unusual. I'd expect GFP_DMA32. All V4L2 drivers u= se > > > > > that. > > > >=20 > > > > GFP_DMA32 had no effect for me on arm64. Probably I need to recheck= . > > >=20 > > > What's the reason to use any specific GFP flags at all? GFP_DMA(32) > > > memory in the guest would typically correspond to host pages without > > > any specific location guarantee. > >=20 > > Typically, but not always, especially for non x86. Say, some platforms > > don't have IOMMUs for codec devices and those devices require physicall= y > > contig low memory. We had to find a way to handle that. >=20 > So basically your hypervisor guarantees that the guest pages inside > the GFP_DMA zone are contiguous and DMA-able on the host as well? > Given the Linux-specific aspect of GFP flags and differences in the > implementation across architectures, perhaps it would be a better idea > to use the DMA mask instead? That wouldn't currently affect vb2_dma_sg > allocations, but in that case the host decoder would have some IOMMU > anyway, right? >=20 DMA mask has no effect for vb2_dma_sg, but GFP has. Unfortunately we need t= o=20 support both of the two: low mem phys contig and low mem sg. So DMA mask=20 cannot be an option. No, there are use-cases with obsolutely no iommus. Best regards, Dmitry. > > Best regards, > > Dmitry. > >=20 > > > Best regards, > > > Tomasz > > >=20 > > > > Best regards, > > > > Dmitry. > > > >=20 > > > > On Donnerstag, 12. M=E4rz 2020 11:18:26 CET Hans Verkuil wrote: > > > > > On 3/12/20 11:15 AM, Dmitry Sepp wrote: > > > > > > Hi Hans, > > > > > >=20 > > > > > > Thank you for your great detailed review! > > > > > >=20 > > > > > > I won't provide inline answers as your comments totally make > > > > > > sense. > > > > > > There > > > > > > is> > > > > > >=20 > > > > > > only one thing I want to mention: > > > > > >>> + struct video_plane_format > > > > > >>> plane_format[VIRTIO_VIDEO_MAX_PLANES]; > > > > > >>=20 > > > > > >> Why is this virtio specific? Any reason for not using > > > > > >> VIDEO_MAX_PLANES? > > > > > >=20 > > > > > > I'd say this is because VIDEO_MAX_PLANES does not exist outside= of > > > > > > the > > > > > > Linux OS, so for whatever other system we need a virtio specifi= c > > > > > > definition. > > > > >=20 > > > > > OK, good reason :-) > > > > >=20 > > > > > It's probably a good thing to add a comment where > > > > > VIRTIO_VIDEO_MAX_PLANES is defined that explains this. > > > > >=20 > > > > > Regards, > > > > >=20 > > > > > Hans --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org