docs: Update the fu540 platform guide for new DT.

With 5.2-rc6 release, Linux kernel hosts the DT for Unleashed board
which is incompatible with the default DT from FSBL.

Update the document to use the DT from kernel.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Acked-by: Anup Patel <anup.patel@wdc.com>

1 files changed, 62 insertions, 50 deletions

diff --git a/docs/platform/sifive_fu540.md b/docs/platform/sifive_fu540.md
index 40ec8d1..2c30e57 100644
--- a/docs/platform/sifive_fu540.md
+++ b/docs/platform/sifive_fu540.md
@@ -11,9 +11,10 @@ Platform Options
 ----------------
 
 As hart0 in the FU540 doesn't have an MMU, only harts 1-4 boot by default.
-A hart mask i.e. *FU540_ENABLED_HART_MASK* compile time option is provided to
-select any other hart for booting. Please keep in mind that this is not
-platform wide option. It can only be specified for FU540 platform in following way.
+A hart mask i.e. *FU540_ENABLED_HART_MASK* compile time option is provided
+to select any other hart for booting. Please keep in mind that this is not
+a generic option and it can only be specified for FU540 platform in the
+following way:
 
 ```
 make PLATFORM=sifive/fu540 FW_PAYLOAD_PATH=Image FU540_ENABLED_HART_MASK=0x02
@@ -23,30 +24,40 @@ This will let the board boot only hart1 instead of default 1-4.
 Building SiFive Fu540 Platform
 -----------------------------
 
-In order to boot SMP Linux in U-Boot, Linux kernel higher than v.5.1-rc1 and
-latest U-Boot(at least HEAD should ffb269ab30db or after) should be used.
+In order to boot SMP Linux in U-Boot, Linux v5.1 (or higher) and latest
+U-Boot v2019.04 (or higher) should be used.
 
 **Linux Kernel Payload**
 
+The HiFive Unleashed device tree(DT) is merged in Linux v5.2 release. This
+DT (device tree) is not backward compatible with the DT passed from FSBL.
+
+To use Linux v5.2 (or higher, the pre-built DTB (DT binary) from Linux v5.2
+(or higher) should be used to build SiFive FU540 OpenSBI binaries by using
+the compile time option *FW_PAYLOAD_FDT_PATH*.
 
 ```
 make PLATFORM=sifive/fu540 FW_PAYLOAD_PATH=<linux_build_directory>/arch/riscv/boot/Image
+or
+(For Linux v5.2 or higher)
+make PLATFORM=sifive/fu540 FW_PAYLOAD_PATH=<linux_build_directory>/arch/riscv/boot/Image FW_PAYLOAD_FDT_PATH=<hifive-unleashed-a00.dtb path from Linux kernel>
 ```
 
 **U-Boot Payload**
 
+The command-line example here assumes that U-Boot was compiled using the
+sifive_fu540_defconfig configuration and with U-Boot v2019.04 (or higher)
+having SMP support.
 
-The command-line example here assumes that U-Boot was compiled using sifive_fu540_defconfig configuration.
-
-With SMP support enabled in U-Boot:
+To use U-Boot which follows Linux v5.2 (or higher) DT bindings, we will
+need custom U-Boot with required driver changes which can be found in
+riscv_unleashed_mmc_spi_v2 branch of https://github.com/avpatel/u-boot.git
 
 ```
 make PLATFORM=sifive/fu540 FW_PAYLOAD_PATH=<u-boot_build_dir>/u-boot.bin
-```
-
-Without SMP support enabled in U-Boot:
-```
-make PLATFORM=sifive/fu540 FW_PAYLOAD_PATH=<u-boot_build_dir>/u-boot.bin FU540_ENABLED_HART_MASK=0x02
+or
+(For U-Boot which follows Linux v5.2 (or higher) DT bindings)
+make PLATFORM=sifive/fu540 FW_PAYLOAD_PATH=<u-boot_build_dir>/u-boot.bin FW_PAYLOAD_FDT_PATH=<hifive-unleashed-a00.dtb path from Linux kernel>
 ```
 
 Generate the uImage from Linux Image.
@@ -58,8 +69,8 @@ mkimage -A riscv -O linux -T kernel -C none -a 0x80200000 -e 0x80200000 -n Linux
 
 **U-Boot & Linux Kernel as a single payload**
 
-A single monolithic image containing both U-Boot & Linux can also be used if network boot setup is
-not available.  
+A single monolithic image containing both U-Boot & Linux can also be used if
+network boot setup is not available.
 
 1. Generate the uImage from Linux Image.
 ```
@@ -68,9 +79,9 @@ mkimage -A riscv -O linux -T kernel -C none -a 0x80200000 -e 0x80200000 -n Linux
 		<linux_build_directory>/arch/riscv/boot/uImage
 ```
 
-2. Create a temporary image with u-boot.bin as the first payload. The command-line
-example here assumes that U-Boot was compiled using sifive_fu540_defconfig
-configuration.
+2. Create a temporary image with u-boot.bin as the first payload. The
+command-line example here assumes that U-Boot was compiled using
+sifive_fu540_defconfig configuration.
 ```
 dd if=~/workspace/u-boot-riscv/u-boot.bin of=/tmp/temp.bin bs=1M
 ```
@@ -81,27 +92,31 @@ dd if=<linux_build_directory>/arch/riscv/boot/uImage of=/tmp/temp.bin bs=1M seek
 4. Compile OpenSBI with temp.bin (generated in step 3) as payload.
 ```
 make PLATFORM=sifive/fu540 FW_PAYLOAD_PATH=/tmp/temp.bin
+or
+(For U-Boot which follows Linux v5.2 (or higher) DT bindings)
+make PLATFORM=sifive/fu540 FW_PAYLOAD_PATH=/tmp/temp.bin FW_PAYLOAD_FDT_PATH=<hifive-unleashed-a00.dtb path from Linux kernel>
 ```
 
 Flashing the OpenSBI firmware binary to storage media:
 -----------------------------------------------------
 The first stage boot loader([FSBL](https://github.com/sifive/freedom-u540-c000-bootloader))
-expects the storage media to have a GPT partition table. It tries to look for a
-partition with following GUID to load the next stage boot loader (OpenSBI in this case).
+expects the storage media to have a GPT partition table. It tries to look for
+a partition with following GUID to load the next stage boot loader (OpenSBI
+in this case).
 
 ```
 2E54B353-1271-4842-806F-E436D6AF6985
-``` 
+```
 
-That's why the generated firmware binary in above steps should be copied to the
-partition of the sdcard with above GUID.
+That's why the generated firmware binary in above steps should be copied to
+the partition of the sdcard with above GUID.
 
 ```
 dd if=build/platform/sifive/fu540/firmware/fw_payload.bin of=/dev/disk2s1 bs=1024
 ```
 
-In my case, it is the first partition is **disk2s1** that has been formatted with the
-above specified GUID.
+In my case, it is the first partition is **disk2s1** that has been formatted
+with the above specified GUID.
 
 In case of a brand new sdcard, it should be formatted with below partition
 tables as described here.
@@ -118,66 +133,62 @@ Booting SiFive Fu540 Platform
 
 **Linux Kernel Payload**
 
-As Linux kernel image is embedded in the OpenSBI firmware binary, HiFive Unleashed will directly
-boot into Linux directly after powered on.
+As Linux kernel image is embedded in the OpenSBI firmware binary, HiFive
+Unleashed will directly boot into Linux directly after powered on.
 
 **U-Boot Payload**
 
-As U-Boot image is used as payload, HiFive Unleashed will boot into a U-Boot prompt.
-U-Boot tftp boot method can be used to load kernel image in U-Boot prompt.
-Here are the steps do a tftpboot.
+As U-Boot image is used as payload, HiFive Unleashed will boot into a U-Boot
+prompt. U-Boot tftp boot method can be used to load kernel image in U-Boot
+prompt. Here are the steps do a tftpboot.
 
 1. Set the mac address of the board.
-
 ```
 setenv ethaddr <mac address of the board>
 ```
-2. Set the ip address of the board.
+(Note: This step is optional)
 
+2. Set the ip address of the board.
 ```
 setenv ipaddr <ipaddr of the board>
 ```
-3. Set the tftpboot server IP.
 
+3. Set the tftpboot server IP.
 ```
 setenv serverip <ipaddr of the tftp server>
 ```
-4. Set the network gateway address.
 
+4. Set the network gateway address.
 ```
 setenv gatewayip <ipaddress of the network gateway>
 ```
-5. Load the Linux kernel image from the tftp server.
 
+5. Load the Linux kernel image from the tftp server.
 ```
 tftpboot ${kernel_addr_r} <uImage path in tftpboot directory>
 ```
 
-6. Load the ramdisk image from the tftp server. This is only required if ramdisk
-   is loaded from tftp server. This step is optional, if rootfs is already part
-   of the kernel or loaded from an external storage by kernel.
-
+6. Load the ramdisk image from the tftp server. This is only required if
+ramdisk is loaded from tftp server. This step is optional, if rootfs is
+already part of the kernel or loaded from an external storage by kernel.
 ```
 tftpboot ${ramdisk_addr_r} <ramdisk path in tftpboot directory>
 ```
-7. Set the boot command-line arguments.
 
+7. Set the boot command-line arguments.
 ```
 setenv bootargs "root=<root partition> rw console=ttySIF0 earlycon=sbi"
 ```
-
-N.B. root partition should point to
-     ** /dev/ram ** - If a ramdisk is used
-     ** root=/dev/mmcblk0pX ** - If a rootfs is already on some other partition of sdcard 
+(Note: root partition should point to
+** /dev/ram ** - If a ramdisk is used
+** root=/dev/mmcblk0pX ** - If a rootfs is already on some other partition
+of sdcard)
 
 8. Now boot into Linux.
-
 ```
 bootm ${kernel_addr_r} ${ramdisk_addr_r} ${fdtcontroladdr}
-
-```
-or (if ramdisk is not loaded from network)
-```
+or
+(If ramdisk is not loaded from network)
 bootm ${kernel_addr_r} - ${fdtcontroladdr}
 ```
 
@@ -188,10 +199,11 @@ At U-Boot prompt execute the following boot command to boot Linux.
 ```
 bootm ${kernel_addr_r} - ${fdtcontroladdr}
 ```
+
 Booting SiFive Fu540 Platform with Microsemi Expansion board
 ------------------------------------------------------------
 
-Until the Linux kernel has in-tree support for device trees and mainline u-boot
+Until the Linux kernel has in-tree support for device trees and upstream U-Boot
 is fully supported on the HiFive Unleashed you can follow these steps to boot
 Linux with the Microsemi expansion board. This method should not be copied on
 future boards and is considered a temporary solution until we can use a more