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

[Phil Elwell]

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>