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

Florian Fainelli
2019-12-06T00:08:18Z

On 12/4/19 4:56 AM, Nicolas Saenz Julienne 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@suse.de>
> ---
>
> NOTE: I'd appreciate if someone from the RPi foundation commented on
> this as it's something that I'll propose to be backported to their tree.

I don't think our additional DTS changes will be merged until -rc1 is
cut, so we have some time to figure this one out. Thanks

>
> arch/arm/boot/dts/bcm2711.dtsi | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm/boot/dts/bcm2711.dtsi b/arch/arm/boot/dts/bcm2711.dtsi
> index 5b61cd915f2b..d6a0e350b7b4 100644
> --- a/arch/arm/boot/dts/bcm2711.dtsi
> +++ b/arch/arm/boot/dts/bcm2711.dtsi
> @@ -43,7 +43,7 @@ soc {
> <0x7c000000 0x0 0xfc000000 0x02000000>,
> <0x40000000 0x0 0xff800000 0x00800000>;
> /* Emulate a contiguous 30-bit address range for DMA */
> - dma-ranges = <0xc0000000 0x0 0x00000000 0x3c000000>;
> + dma-ranges = <0xc0000000 0x0 0x00000000 0x40000000>;
>
> /*
> * This node is the provider for the enable-method for
>

--
Florian