doc: update UEFI documentation

* UEFI variables can be persisted
* describe that the sequence of files loaded before bootefi matters

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

diff --git a/doc/uefi/uefi.rst b/doc/uefi/uefi.rst
index a72e729cc82cca1f250fec65116db00d76914e4c..728f7bf4e0a3fb49772b603d91bfe8c55215885b 100644 (file)
--- a/doc/uefi/uefi.rst
+++ b/doc/uefi/uefi.rst
@@ -59,6 +59,10 @@ Below you find the output of an example session starting GRUB::
     120832 bytes read in 7 ms (16.5 MiB/s)
     => bootefi ${kernel_addr_r} ${fdt_addr_r}
 
+The bootefi command uses the device, the file name, and the file size
+(environment variable 'filesize') of the most recently loaded file when setting
+up the binary for execution. So the UEFI binary should be loaded last.
+
 The environment variable 'bootargs' is passed as load options in the UEFI system
 table. The Linux kernel EFI stub uses the load options as command line
 arguments.
@@ -217,13 +221,13 @@ which has to be enabled via CONFIG_SUPPORT_EMMC_RPMB=y.
 Executing the boot manager
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-The UEFI specification foresees to define boot entries and boot sequence via UEFI
-variables. Booting according to these variables is possible via::
+The UEFI specification foresees to define boot entries and boot sequence via
+UEFI variables. Booting according to these variables is possible via::
 
     bootefi bootmgr [fdt address]
 
-As of U-Boot v2018.03 UEFI variables are not persisted and cannot be set at
-runtime.
+As of U-Boot v2020.10 UEFI variables cannot be set at runtime. The U-Boot
+command 'efidebug' can be used to set the variables.
 
 Executing the built in hello world application
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~