Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-ID: <41607c9fc20afc6554d697daa7782de1e3281db7.camel@suse.de>
Subject: Re: [PATCH] arm64: mm: make CONFIG_ZONE_DMA configurable without
 EXPERT
From:   Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To:     Peng Fan <peng.fan@nxp.com>,
        Catalin Marinas <catalin.marinas@arm.com>
Cc:     "will@kernel.org" <will@kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        dl-linux-imx <linux-imx@nxp.com>,
        Robin Murphy <robin.murphy@arm.com>
Date:   Fri, 27 Mar 2020 12:17:59 +0100
In-Reply-To: <AM0PR04MB4481C3A233AB455BDC68736288CE0@AM0PR04MB4481.eurprd04.prod.outlook.com>
References: <1583844526-24229-1-git-send-email-peng.fan@nxp.com>
         <20200324174134.GH3901@mbp>
         <AM0PR04MB44819E95EB1FABF09DEE682788CE0@AM0PR04MB4481.eurprd04.prod.outlook.com>
         <20200325101652.GJ3901@mbp>
         <AM0PR04MB4481C3A233AB455BDC68736288CE0@AM0PR04MB4481.eurprd04.prod.outlook.com>
Content-Type: multipart/signed; micalg="pgp-sha256";
        protocol="application/pgp-signature"; boundary="=-gybhYNbk/O36qUlXjYkF"
User-Agent: Evolution 3.34.4 
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


--=-gybhYNbk/O36qUlXjYkF
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Hi Peng,

On Wed, 2020-03-25 at 12:30 +0000, Peng Fan wrote:
> > > > I see a few potential options:
> > > >=20
> > > > a) Ensure the CMA is contained within a single zone.
> > >=20
> > > This will break legacy dts with new version kernel.
> > >=20
> > > > How large is it in your case?
> > >=20
> > > It is 1GB
> > >=20
> > > > Is it allocated by the kernel dynamically or a fixed start set by
> > > > the boot loader?
> > >=20
> > > We use alloc-ranges and size in kernel dts.
> > >=20
> > > But there is only 2GB DRAM in the board.
> >=20
> > So I guess without changing the dts, option (a) doesn't really work.
> >=20
> > > > b) Change the CMA allocator to allow spanning multiple zones (last =
time
> > > >    I looked it wasn't trivial since it relied on some per-zone lock=
).

I like this as a solution, ultimately why should CMA be linked to a specifi=
c
zone. Also, crossing the ZONE_DMA/ZONE_DMA32 boundary shouldn't be an issue
since we already default to ZONE_DMA32 as the default area for CMA.

That said, easier said than done.

> > > > c) Make ZONE_DMA dynamic on arm64 and only enable it if RPi4.
> > >=20
> > > Option c seems a bit easier to me :)
> > >=20
> > > I will try to explore both, but if you have time to help, that would
> > > be appreciated.
> >=20
> > I don't have time but option (c) was already discussed and there are pa=
tches
> > from Nicolas on the list:
> >=20
> > https://eur01.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Flor=
e.ke
> > rnel.org%2Flinux-arm-kernel%2F20190820145821.27214-5-nsaenzjulienne%
> > 40suse.de%2F&amp;data=3D02%7C01%7Cpeng.fan%40nxp.com%7C6403ddf37
> > 89b452ae5ee08d7d0a5a659%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0
> > %7C0%7C637207282191026738&amp;sdata=3Dt2cZ9HTCcRuaL9RO4kD%2BzN
> > 2n4VqM%2F66zYNZIOComCVs%3D&amp;reserved=3D0
> >=20
> > The above series was checking whether the platform is RPi4 and limiting=
 the
> > ZONE_DMA size to 1GB (otherwise 4GB with ZONE_DMA32 empty). We
> > ended up with a static 1GB for ZONE_DMA but we missed the fact that it =
may
> > break existing platforms.
>=20
> Thanks for the information. I'll check the patchset and work out somethin=
g
> proper to fix the issue I met.

Just an FYI, I'm follwing the conversation, and will try to look into as so=
on
as I get some free time. In the meantime if you want me to test/review anyt=
hing
on the Raspberry Pi, I'll be happy to.

Regards,
Nicolas


--=-gybhYNbk/O36qUlXjYkF
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: This is a digitally signed message part
Content-Transfer-Encoding: 7bit

-----BEGIN PGP SIGNATURE-----

iQEzBAABCAAdFiEErOkkGDHCg2EbPcGjlfZmHno8x/4FAl594OcACgkQlfZmHno8
x/7e1gf/UtbHfYf9EO36liu7HDv+5r0zCa19nQ64rn/FN46GJbl++HyRBerEwig7
L8pNRHFamul6BolfWHLJE1e4gSBAOlt5oJph7vK0/cGXoownZHGfjy4ygBgbj2Zc
Tf8YTBV1bTWWSPEjsdBbjNUMrxqtVkr+13NXs5yb4hxnKX7OAFf9YLyNOiTSk3yU
XgMIgwWuMQZ8FR290WAghA/wmBUfTEVJJ/rbi34xlQnBGaUZpwqR87SE/hGoNpoW
qv4kci3ttdJ3yX7IvTqnsYEJ7ThMbYmhwH8Tk7tuKi2C/zqTpzgajvfDtA6MDMCN
87b41meteMRHPKf+eqhUU2s+meQCYA==
=hASN
-----END PGP SIGNATURE-----

--=-gybhYNbk/O36qUlXjYkF--