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

Phil Elwell
2019-12-06T10:16:14Z

Hi Nicolas,

On 06/12/2019 00:08, Florian Fainelli wrote:
> 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.

The 0x3c000000 size was a mistake that arose from c0000000 + 3c000000 =
fc000000, but that is mixing apples and oranges (actually DMA addresses
and host physical addresses). Please correct it as you are proposing.

>
> 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
>>
>
>