[PATCH 2/2] ARM: i.MX8MM: add reboot to serial download mode

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

The i.MX8MM reference manual follows long established tradition in not
documenting BootROM magic reboot codes. For older i.MX variants, the
values can be seen in the bmode tables of Freescale's U-Boot patches.

There are no such patches for the i.MX8M, but testing shows that

	mw 0x30390094 0x10 ; mw 0x30390098 0x40000000

is one of the configurations that trigger serial download on next warm
reset on an i.MX8MM. Describe this in the device tree, so

	gpr.reboot_mode.next=serial reset -r imxwd-warm

does the right thing for that SoC.

This all might work for other i.MX8M variants as well, but the dtsi
can be genericized later on when tested.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
Cc: David Jander <david@protonic.nl>
Cc: Lucas Stach <l.stach@pengutronix.de>
---
 Documentation/boards/imx.rst   | 29 +++++++++++++++++++++++++++++
 arch/arm/dts/imx8mm-evk.dts    |  1 +
 arch/arm/dts/imx8mm-prt8mm.dts |  1 +
 arch/arm/dts/imx8mm.dtsi       | 18 ++++++++++++++++++
 4 files changed, 49 insertions(+)
 create mode 100644 arch/arm/dts/imx8mm.dtsi

diff --git a/Documentation/boards/imx.rst b/Documentation/boards/imx.rst
index 887b45c70881..4ce9d9808cc1 100644
--- a/Documentation/boards/imx.rst
+++ b/Documentation/boards/imx.rst
@@ -83,6 +83,35 @@ The images can also always be started as second stage on the target:
 
   barebox@Board Name:/ bootm /mnt/tftp/barebox-freescale-imx51-babbage.img
 
+BootROM Reboot mode codes (bmode)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+For select SoCs, barebox supports communicating an alternative boot medium
+that BootROM should select after a warm reset::
+
+  barebox@FSL i.MX8MM EVK board:/ devinfo gpr.reboot_mode
+  Driver: syscon-reboot-mode
+  Bus: platform
+  Parent: 30390000.reset-controller@30390000.of
+  Parameters:
+    next: normal (type: enum) (values: "normal", "serial")
+    prev: normal (type: enum) (values: "normal", "serial")
+  Device node: /soc@0/bus@30000000/reset-controller@30390000/reboot-mode
+  reboot-mode {
+          compatible = "barebox,syscon-reboot-mode";
+          offset = <0x94 0x98>;
+          mask = <0xffffffff 0x40000000>;
+          mode-normal = <0x0 0x0>;
+          mode-serial = <0x10 0x40000000>;
+  };
+
+  barebox@FSL i.MX8MM EVK board:/ gpr.reboot_mode.next=serial reset -r imxwd-warm
+
+This will cause barebox to fall into serial download mode on an i.MX8MM.
+
+Different SoCs may have more possible reboot modes available.
+See the section on :ref:`Reboot modes<reboot_mode>` for more information.
+
 High Assurance Boot
 ^^^^^^^^^^^^^^^^^^^
 
diff --git a/arch/arm/dts/imx8mm-evk.dts b/arch/arm/dts/imx8mm-evk.dts
index 1e8619ccf584..304f150307a3 100644
--- a/arch/arm/dts/imx8mm-evk.dts
+++ b/arch/arm/dts/imx8mm-evk.dts
@@ -7,6 +7,7 @@
 /dts-v1/;
 
 #include <arm64/freescale/imx8mm-evk.dts>
+#include "imx8mm.dtsi"
 
 / {
 	chosen {
diff --git a/arch/arm/dts/imx8mm-prt8mm.dts b/arch/arm/dts/imx8mm-prt8mm.dts
index bdcdd0806243..abd758f2856e 100644
--- a/arch/arm/dts/imx8mm-prt8mm.dts
+++ b/arch/arm/dts/imx8mm-prt8mm.dts
@@ -7,6 +7,7 @@
 /dts-v1/;
 
 #include <arm64/freescale/imx8mm.dtsi>
+#include "imx8mm.dtsi"
 
 / {
 	model = "Protonic PRT8MM";
diff --git a/arch/arm/dts/imx8mm.dtsi b/arch/arm/dts/imx8mm.dtsi
new file mode 100644
index 000000000000..78bbacb2b1b2
--- /dev/null
+++ b/arch/arm/dts/imx8mm.dtsi
@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+/ {
+	aliases {
+		gpr.reboot_mode = &reboot_mode_gpr;
+	};
+};
+
+&src {
+	compatible = "fsl,imx8mm-src", "fsl,imx8mq-src", "syscon", "simple-mfd";
+
+	reboot_mode_gpr: reboot-mode {
+		compatible = "barebox,syscon-reboot-mode";
+		offset = <0x94>, <0x98>; /* SRC_GPR{9,10} */
+		mask = <0xffffffff>, <0x40000000>;
+		mode-normal = <0>, <0>;
+		mode-serial = <0x00000010>, <0x40000000>;
+	};
+};
-- 
2.30.2


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