rockchip: rk3399: spl: make SPL boot-order configurable via /chosen

The RK3399 does not have any boot selection pins and the BootROM probes
the boot interfaces using the following boot-order:
    1. SPI
    2. eMMC (sdhci in DTS)
    3. SD card (sdmmc in DTS)
    4. USB loader
For ease of deployment, the SPL stage should mirror the boot order of
the ROM and use the same probing order (assuming that valid images can
be detected by SPL) unless instructed otherwise.  The boot-order can
then be configured via the 'u-boot,spl-boot-order' property in the
chosen-node of the DTS.

While this approach is easily extensible to other boards, it is only
implemented for the RK3399 for now, as the large SRAM on the RK3399
makes this easy to fit the needed infrastructure into SPL and our
production setup already runs with DM, OF_CONTROL and BLK in SPL.

The new boot-order property is expected to be used in conjunction with
FIT images (and all legacy image formats disabled via Kconfig).

A boot-sequence with probing and fallthroughs from SPI via eMMC to SD
card (i.e. &spiflash, &sdhci, &sdmmc) has been validated on the RK3399-Q7.

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Tested-by: Klaus Goger <klaus.goger@theobroma-systems.com>
Tested-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Simon Glass <sjg@chromium.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/doc/device-tree-bindings/chosen.txt b/doc/device-tree-bindings/chosen.txt
index bf9a30a..5625d21 100644
--- a/doc/device-tree-bindings/chosen.txt
+++ b/doc/device-tree-bindings/chosen.txt
@@ -41,3 +41,25 @@ Example
 		reg = <0xf00 0x10>;
 	};
 };
+
+u-boot,spl-boot-order property
+------------------------------
+
+In a system using an SPL stage and having multiple boot sources
+(e.g. SPI NOR flash, on-board eMMC and a removable SD-card), the boot
+device may be probed by reading the image and verifying an image
+signature.
+
+If the SPL is configured through the device-tree, the boot-order can
+be configured with the spl-boot-order property under the /chosen node.
+Each list element of the property should specify a device to be probed
+in the order they are listed: references (i.e. implicit paths), a full
+path or an alias is expected for each entry.
+
+Example
+-------
+/ {
+	chosen {
+		u-boot,spl-boot-order = &sdmmc, "/sdhci@fe330000";
+	};
+};