linux-kernel - Re: [PATCH] ARM: dts: bcm2711: fix soc's node dma-ranges

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Date:   Mon,  9 Dec 2019 10:12:56 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     bcm-kernel-feedback-list@...adcom.com,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Eric Anholt <eric@...olt.net>, Stefan Wahren <wahrenst@....net>
Cc:     mbrugger@...e.com, phil@...pberrypi.org,
        devicetree@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: bcm2711: fix soc's node dma-ranges

On Wed,  4 Dec 2019 13:56:33 +0100, Nicolas Saenz Julienne <nsaenzjulienne@...e.de> wrote:
> Raspberry Pi's firmware has a feature to select how much memory to
> reserve for its GPU called 'gpu_mem'. The possible values go from 16MB
> to 944MB, with a default of 64MB. This memory resides in the topmost
> part of the lower 1GB memory area and grows bigger expanding towards the
> begging of memory.
> 
> It turns out that with low 'gpu_mem' values (16MB and 32MB) the size of
> the memory available to the system in the lower 1GB area can outgrow the
> interconnect's dma-range as its size was selected based on the maximum
> system memory available given the default gpu_mem configuration. This
> makes that memory slice unavailable for DMA. And may cause nasty kernel
> warnings if CMA happens to include it.
> 
> Change soc's dma-ranges to really reflect it's HW limitation, which is
> being able to only DMA to the lower 1GB area.
> 
> Fixes: 7dbe8c62ceeb ("ARM: dts: Add minimal Raspberry Pi 4 support")
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
> ---

Applied to devicetree/fixes, thanks!
--
Florian