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

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Message-ID: <69c2f4ac-896d-4cfc-8068-45bd58aef6dd@broadcom.com>
Date: Mon, 14 Oct 2024 10:10:11 -0700
From: Florian Fainelli <florian.fainelli@...adcom.com>
To: Bjorn Helgaas <helgaas@...nel.org>, Stanimir Varbanov <svarbanov@...e.de>
Cc: linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-rpi-kernel@...ts.infradead.org,
 linux-pci@...r.kernel.org,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, Thomas Gleixner
 <tglx@...utronix.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Jim Quinlan <jim2101024@...il.com>,
 Nicolas Saenz Julienne <nsaenz@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, kw@...ux.com,
 Philipp Zabel <p.zabel@...gutronix.de>,
 Andrea della Porta <andrea.porta@...e.com>,
 Phil Elwell <phil@...pberrypi.com>, Jonathan Bell <jonathan@...pberrypi.com>
Subject: Re: [PATCH v3 04/11] PCI: brcmstb: Expand inbound size calculation
 helper

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?
-- 
Florian