On 06/12/2019 18:13, Florian Fainelli wrote:
On 12/6/19 2:16 AM, Phil Elwell wrote:
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@xxxxxxx>
---
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.
Do you want to add an Acked-by or Reviewed-by tag to make this statement
official?
Here you go:
Reviewed-by: Phil Elwell <phil@xxxxxxxxxxxxxxx>
