Re: [PATCH v3 04/11] PCI: brcmstb: Expand inbound size calculation helper

Jim Quinlan
2024-10-16T17:10:54Z

On Mon, Oct 14, 2024 at 1:25 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> On Mon, Oct 14, 2024 at 10:10:11AM -0700, Florian Fainelli wrote:
> > On 10/14/24 09:57, Bjorn Helgaas wrote:
> > > On Mon, Oct 14, 2024 at 04:07:03PM +0300, Stanimir Varbanov wrote:
> > > > BCM2712 memory map can supports up to 64GB of system
> > > > memory, thus expand the inbound size calculation in
> > > > helper function up to 64GB.
> > >
> > > The fact that the calculation is done in a helper isn't important
> > > here. Can you make the subject line say something about supporting
> > > DMA for up to 64GB of system memory?
> > >
> > > This is being done specifically for BCM2712, but I assume it's safe
> > > for *all* brcmstb devices, right?
> >
> > It is safe in the sense that all brcmstb devices with this PCIe controller
> > will adopt the same encoding of the size, all of the currently supported
> > brcmstb devices have a variety of limitations when it comes to the amount of
> > addressable DRAM however. Typically we have a hard limit at 4GB of DRAM per
> > memory controller, some devices can do 2GB x3, 4GB x2, or 4GB x1.
> >
> > Does that answer your question?
>
> I'd like something in the commit log to the effect that while we're
> doing this to support more system memory on BCM2712, this change is
> safe for other SoCs that don't support as much system memory.

Hello,

This setting configures the size of an RC's inbound window to system
memory. Any inbound access outside of all of the
inbound windows will be discarded.

Some existing SoCs cannot support the 64GB size. Configuring such an
SoC to 64GB
will effectively disable the entire window.

Regards,
Jim Quinlan
Broadcom STB/CM