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

On Mon, Oct 14, 2024 at 1:25 PM Bjorn Helgaas [off-list ref] wrote:

On Mon, Oct 14, 2024 at 10:10:11AM -0700, Florian Fainelli wrote:

quoted

On 10/14/24 09:57, Bjorn Helgaas wrote:

quoted

On Mon, Oct 14, 2024 at 04:07:03PM +0300, Stanimir Varbanov wrote:

quoted

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