linux-kernel - Re: [PATCH 1/2] ARM: dts: bcm2711: force CMA into first GB of memory

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Message-ID: <20191105145150.GB22987@arrakis.emea.arm.com>
Date:   Tue, 5 Nov 2019 14:51:50 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Stefan Wahren <wahrenst@....net>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        devicetree@...r.kernel.org, bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Eric Anholt <eric@...olt.net>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] ARM: dts: bcm2711: force CMA into first GB of memory

On Mon, Nov 04, 2019 at 06:09:39PM +0100, Stefan Wahren wrote:
> Hi Nicolas,
> 
> Am 04.11.19 um 14:54 schrieb Nicolas Saenz Julienne:
> > arm64 places the CMA in ZONE_DMA32, which is not good enough for the
> > Raspberry Pi 4 since it contains peripherals that can only address the
> > first GB of memory. Explicitly place the CMA into that area.
> >
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> 
> do you want this in Linux 5.5 via devicetree/fixes? In this case please
> add an fixes tag.

That's not really a fix since AFAICT CMA never worked properly on RPi4
with mainline. For 5.5, I queued the arm64 for-next/zone-dma patches
which would allow RPi4 to get a CMA in the correct physical address
range. However, since these patches cause a regression on other
platforms that don't need a small ZOEN_DMA, my suggestion was to leave
the CMA handling for RPi4 as per the current mainline (i.e. broken) and
allow CMA from the full ZONE_DMA32 range (second patch in this series).

IIUC, this dts patch can be merged independently of the ZONE_DMA patches
for arm64 and it may be beneficial for current mainline (even without
the arm64/for-next/zone-dma patches).

[1] git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux for-next/zone-dma

> Otherwise this will be queued for Linux 5.6.

I'm happy to queue them together with your ack for 5.5, otherwise I'll
only pick the second patch in this series.

Thanks.

-- 
Catalin