[SRU][F/raspi][PATCH 2/2] overlays: Add pcie-32bit-dma overlay

[Juerg Haefliger]

From: Nicolas Saenz Julienne <nsaenzjulienne at suse.de>

BugLink: https://bugs.launchpad.net/bugs/1927037

In order to accommodate full PCI DMA access to memory on newer BCM2711
revisions, we're forced to map PCIe's view of physical memory with an
offset. This offset makes DMA addressing dependent on having 64bit
support on the PCI device's side. Which isn't always the case.

In order to mitigate this, introduce the pcie-32bit-dma overlay which
will forbid firmware from updating the default inbound memory window.
The default setting, albeit limited to accessing the lower 3GB of
memory, will allow for 32bit DMA addresses at the expense of having to
bounce buffers.

Link: https://github.com/raspberrypi/linux/issues/4197
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne at suse.de>

(cherry picked from commit 2c51556df1be8d1a72a207da277d648cfef40fd4 rpi-5.11.y)
Signed-off-by: Juerg Haefliger <juergh at canonical.com>
---
 arch/arm/boot/dts/overlays/Makefile            |  1 +
 arch/arm/boot/dts/overlays/README              |  7 +++++++
 arch/arm/boot/dts/overlays/overlay_map.dts     |  4 ++++
 .../dts/overlays/pcie-32bit-dma-overlay.dts    | 18 ++++++++++++++++++
 4 files changed, 30 insertions(+)
 create mode 100644 arch/arm/boot/dts/overlays/pcie-32bit-dma-overlay.dts

diff --git a/arch/arm/boot/dts/overlays/Makefile b/arch/arm/boot/dts/overlays/Makefile
index b6abddcb2615..ae2ff52c9275 100644
--- a/arch/arm/boot/dts/overlays/Makefile
+++ b/arch/arm/boot/dts/overlays/Makefile
@@ -126,6 +126,7 @@ dtbo-$(CONFIG_ARCH_BCM2835) += \
 	ov9281.dtbo \
 	papirus.dtbo \
 	pca953x.dtbo \
+	pcie-32bit-dma.dtbo \
 	pibell.dtbo \
 	pifacedigital.dtbo \
 	pifi-40.dtbo \
diff --git a/arch/arm/boot/dts/overlays/README b/arch/arm/boot/dts/overlays/README
index f3d6bf57f40b..03fdbdbe4729 100644
--- a/arch/arm/boot/dts/overlays/README
+++ b/arch/arm/boot/dts/overlays/README
@@ -2055,6 +2055,13 @@ Params: addr                    I2C address of expander. Default 0x20.
         xra1202                 Select the Exar XRA1202 (8 bit)
 
 
+Name:   pcie-32bit-dma
+Info:   Force PCIe config to support 32bit DMA addresses at the expense of
+        having to bounce buffers.
+Load:   dtoverlay=pcie-32bit-dma
+Params: <None>
+
+
 [ The pcf2127-rtc overlay has been deleted. See i2c-rtc. ]
 
 
diff --git a/arch/arm/boot/dts/overlays/overlay_map.dts b/arch/arm/boot/dts/overlays/overlay_map.dts
index b2e6b41216b2..e9a15fab82c7 100644
--- a/arch/arm/boot/dts/overlays/overlay_map.dts
+++ b/arch/arm/boot/dts/overlays/overlay_map.dts
@@ -37,6 +37,10 @@
 		deprecated = "use gpio-ir";
 	};
 
+	pcie-32bit-dma {
+		bcm2711;
+	};
+
 	pi3-act-led {
 		renamed = "act-led";
 	};
diff --git a/arch/arm/boot/dts/overlays/pcie-32bit-dma-overlay.dts b/arch/arm/boot/dts/overlays/pcie-32bit-dma-overlay.dts
new file mode 100644
index 000000000000..cca3e83721b7
--- /dev/null
+++ b/arch/arm/boot/dts/overlays/pcie-32bit-dma-overlay.dts
@@ -0,0 +1,18 @@
+/*
+ * pcie-32bit-dma-overlay.dts
+ */
+
+/dts-v1/;
+/plugin/;
+
+/ {
+	compatible = "brcm,bcm2711";
+
+	fragment at 0 {
+		target-path = "/aliases";
+		__overlay__ {
+			pcie0 = "";
+		};
+	};
+
+};
-- 
2.27.0