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Message-ID: <8140975aa1f5c3cbdfa2e6f42aecebe3701f29da.camel@ndufresne.ca>
Subject: Re: [PATCH 3/9] dma-heap: Provide accessors so that in-kernel
 drivers can allocate dmabufs from specific heaps
From:   Nicolas Dufresne <nicolas@ndufresne.ca>
To:     Christian =?ISO-8859-1?Q?K=F6nig?= 
        <ckoenig.leichtzumerken@gmail.com>,
        Yong Wu =?UTF-8?Q?=28=E5=90=B4=E5=8B=87=29?= 
        <Yong.Wu@mediatek.com>, "jstultz@google.com" <jstultz@google.com>
Cc:     "sumit.semwal@linaro.org" <sumit.semwal@linaro.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "robh+dt@kernel.org" <robh+dt@kernel.org>,
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        Jianjiao Zeng =?UTF-8?Q?=28=E6=9B=BE=E5=81=A5=E5=A7=A3=29?= 
        <Jianjiao.Zeng@mediatek.com>,
        Kuohong Wang =?UTF-8?Q?=28=E7=8E=8B=E5=9C=8B=E9=B4=BB=29?= 
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Date:   Tue, 12 Sep 2023 10:58:45 -0400
In-Reply-To: <95797f3d-65bf-1bd9-9e19-6de42605cfe3@gmail.com>
References: <20230911023038.30649-1-yong.wu@mediatek.com>
         <20230911023038.30649-4-yong.wu@mediatek.com>
         <803846bc-fd1d-d2ec-2855-456af22c82f8@amd.com>
         <CANDhNCrQyiFZ+8DnG0iyKBXC0H1698K1a9d2AxOq4whDsZBn+Q@mail.gmail.com>
         <23e71d1f-08c1-3834-5b1f-2b5714c7bfaa@gmail.com>
         <255ae6b9ac1b6bea9262069747824b8461475e70.camel@mediatek.com>
         <95797f3d-65bf-1bd9-9e19-6de42605cfe3@gmail.com>
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Le mardi 12 septembre 2023 =C3=A0 16:46 +0200, Christian K=C3=B6nig a =C3=
=A9crit=C2=A0:
> Am 12.09.23 um 10:52 schrieb Yong Wu (=E5=90=B4=E5=8B=87):
> > [SNIP]
> > > But what we should try to avoid is that newly merged drivers provide
> > > both a driver specific UAPI and DMA-heaps. The justification that
> > > this
> > > makes it easier to transit userspace to the new UAPI doesn't really
> > > count.
> > >=20
> > > That would be adding UAPI already with a plan to deprecate it and
> > > that
> > > is most likely not helpful considering that UAPI must be supported
> > > forever as soon as it is upstream.
> > Sorry, I didn't understand this. I think we have not change the UAPI.
> > Which code are you referring to?
>=20
> Well, what do you need this for if not a new UAPI?
>=20
> My assumption here is that you need to export the DMA-heap allocation=20
> function so that you can server an UAPI in your new driver. Or what else=
=20
> is that good for?
>=20
> As far as I understand you try to upstream your new vcodec driver. So=20
> while this change here seems to be a good idea to clean up existing=20
> drivers it doesn't look like a good idea for a newly created driver.

MTK VCODEC has been upstream for quite some time now. The other patchset is
trying to add secure decoding/encoding support to that existing upstream dr=
iver.

Regarding the uAPI, it seems that this addition to dmabuf heap internal API=
 is
exactly the opposite. By making heaps available to drivers, modification to=
 the
V4L2 uAPI is being reduced to adding "SECURE_MODE" + "SECURE_HEAP_ID" contr=
ols
(this is not debated yet has an approach). The heaps is being used internal=
ly in
replacement to every allocation, user visible or not.

Nicolas

>=20
> Regards,
> Christian.
>=20
> > > > So I think this patch is a little confusing in this series, as I
> > > don't
> > > > see much of it actually being used here (though forgive me if I'm
> > > > missing it).
> > > >=20
> > > > Instead, It seems it get used in a separate patch series here:
> > > >    =20
> > > https://lore.kernel.org/all/20230911125936.10648-1-yunfei.dong@mediat=
ek.com/
> > >=20
> > > Please try to avoid stuff like that it is really confusing and eats
> > > reviewers time.
> > My fault, I thought dma-buf and media belonged to the different tree,
> > so I send them separately. The cover letter just said "The consumers of
> > the new heap and new interface are our codecs and DRM, which will be
> > sent upstream soon", and there was no vcodec link at that time.
> >=20
> > In the next version, we will put the first three patches into the
> > vcodec patchset.
> >=20
> > Thanks.
> >=20
>=20