linux-kernel - Re: [PATCH v5 1/7] arm64: dts: qcom: sc7280: Increase config size to 256MB for ECAM feature

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Message-ID: <h6bnt7ti3yy3welkzqwia7kieunspfqtxf6k46t4j4d5tathls@hra2gbpzazep>
Date: Fri, 28 Mar 2025 17:14:35 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>, 
	cros-qcom-dts-watchers@...omium.org, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kw@...ux.com>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Jingoo Han <jingoohan1@...il.com>, linux-arm-msm@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, 
	quic_vbadigan@...cinc.com, quic_mrana@...cinc.com, quic_vpernami@...cinc.com, 
	mmareddy@...cinc.com
Subject: Re: [PATCH v5 1/7] arm64: dts: qcom: sc7280: Increase config size to
 256MB for ECAM feature

On Wed, Mar 26, 2025 at 06:56:02PM +0100, Konrad Dybcio wrote:
> On 3/11/25 12:13 PM, Konrad Dybcio wrote:
> > On 3/9/25 6:45 AM, Krishna Chaitanya Chundru wrote:
> >> PCIe ECAM(Enhanced Configuration Access Mechanism) feature requires
> >> maximum of 256MB configuration space.
> >>
> >> To enable this feature increase configuration space size to 256MB. If
> >> the config space is increased, the BAR space needs to be truncated as
> >> it resides in the same location. To avoid the bar space truncation move
> >> config space, DBI, ELBI, iATU to upper PCIe region and use lower PCIe
> >> iregion entirely for BAR region.
> >>
> >> This depends on the commit: '10ba0854c5e6 ("PCI: qcom: Disable mirroring
> >> of DBI and iATU register space in BAR region")'
> >>
> >> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> >> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> >> ---
> > 
> > Reviewed-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
> 
> I took a second look - why are dbi and config regions overlapping?
> 

Not just DBI, ELBI too.

> I would imagine the latter to be at a certain offset
> 

The problem is that for ECAM, we need config space region to be big enough to
cover all 256 buses. For that reason Krishna overlapped the config region and
DBI/ELBI. Initially I also questioned this and somehow convinced that there is
no other way (no other memory). But looking at the internal documentation now,
I realized that atleast 512MiB of PCIe space is available for each controller
instance.

So I just quickly tried this series on SA8775p and by moving the config space
after the iATU region, I was able to have ECAM working without overlapping
addresses in DT. Here is the change I did:

diff --git a/arch/arm64/boot/dts/qcom/sa8775p.dtsi b/arch/arm64/boot/dts/qcom/sa8775p.dtsi
index 3394ae2d1300..e41c8e3dd30c 100644
--- a/arch/arm64/boot/dts/qcom/sa8775p.dtsi
+++ b/arch/arm64/boot/dts/qcom/sa8775p.dtsi
@@ -6395,18 +6395,18 @@ arch_timer: timer {
        pcie0: pcie@...0000 {
                compatible = "qcom,pcie-sa8775p";
                reg = <0x0 0x01c00000 0x0 0x3000>,
-                     <0x0 0x40000000 0x0 0xf20>,
-                     <0x0 0x40000f20 0x0 0xa8>,
-                     <0x0 0x40001000 0x0 0x4000>,
-                     <0x0 0x40100000 0x0 0x100000>,
+                     <0x4 0x00000000 0x0 0xf20>,
+                     <0x4 0x00000f20 0x0 0xa8>,
+                     <0x4 0x10000000 0x0 0x4000>,
+                     <0x4 0x10004000 0x0 0x10000000>,
                      <0x0 0x01c03000 0x0 0x1000>;
                reg-names = "parf", "dbi", "elbi", "atu", "config", "mhi";
                device_type = "pci";
 
                #address-cells = <3>;
                #size-cells = <2>;
-               ranges = <0x01000000 0x0 0x00000000 0x0 0x40200000 0x0 0x100000>,
-                        <0x02000000 0x0 0x40300000 0x0 0x40300000 0x0 0x1fd00000>;
+               ranges = <0x01000000 0x0 0x00000000 0x0 0x40000000 0x0 0x100000>,
+                        <0x02000000 0x0 0x40100000 0x0 0x40100000 0x0 0x1ff00000>;
                bus-range = <0x00 0xff>;
 
                dma-coherent;
 

Krishna: Could you also try similar change on SC7280 and see if it works?

- Mani

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