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From: Andy Duan <fugang.duan@nxp.com>
Subject: RE: [rpmsg PATCH v2 1/1] rpmsg: virtio_rpmsg_bus: fix unexpected huge
 vmap mappings
Date: Wed, 16 Jan 2019 03:38:38 +0000
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To: Christoph Hellwig <hch@infradead.org>
Cc: "bjorn.andersson@linaro.org" <bjorn.andersson@linaro.org>, "ohad@wizery.com" <ohad@wizery.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Andrew Morton <akpm@linux-foundation.org>, Linux-MM <linux-mm@kvack.org>, Robin Murphy <robin.murphy@arm.com>, "linux-remoteproc@vger.kernel.org" <linux-remoteproc@vger.kernel.org>, "anup@brainfault.org" <anup@brainfault.org>, "loic.pallardy@st.com" <loic.pallardy@st.com>, dl-linux-imx <linux-imx@nxp.com>, Richard Zhu <hongxing.zhu@nxp.com>, Jason Liu <jason.hui.liu@nxp.com>, Peng Fan <peng.fan@nxp.com>

From: Christoph Hellwig <hch@infradead.org> Sent: Monday, January 14, 2019 =
5:53 PM
> On Fri, Jan 11, 2019 at 01:28:46AM +0000, Andy Duan wrote:
> > As NXP i.MX8 platform requirement that M4 only access the fixed memory
> > region, so do You have any suggestion to fix the issue and satisfy the
> > requirement ? Or do you have plan To fix the root cause ?
>=20
> I think the answer is to use RESERVEDMEM_OF_DECLARE without the DMA
> coherent boilerplate code.
If use RESERVEDMEM_OF_DECLARE with DMA contiguous code (CMA), it can
match the requirement, but as you know, the CMA size alignment is 32M bytes=
,
we only need 8M bytes contiguous mem for rpmsg.

>=20
> For the initial prototype just do it inside the driver, although I'd like=
 to
> eventually factor this out into common code, especially if my proposal fo=
r
> more general availability of DMA_ATTR_NON_CONSISTENT goes ahead.