env: mmc: statically set the environment partition name

The new opt-out setting, CONFIG_ENV_MMC_PARTITION, statically sets
the MMC environment partition name. Prior to this patch, the only way
to declare this partition name was by creating a
'u-boot,mmc-env-partition' parameter in the device-tree's /config node.

This setting provides additional flexibility, particularly in cases
where accessing the device-tree is not straightforward (e.g. QEMU).

If undeclared, the device-tree's setting will be used.

Signed-off-by: Emmanuel Di Fede <emmanuel.difede@cysec.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>

doc/device-tree-bindings/config.txt

@@ -76,6 +76,8 @@ u-boot,mmc-env-partition (int)
 	precedence. In that case, only if the partition is not found,
 	mmc-env-offset* will be tried.
 
+	Note that CONFIG_ENV_MMC_PARTITION overrides this device-tree setting.
+
 u-boot,no-apm-finalize (bool)
 	For x86 devices running on coreboot, this tells U-Boot not to lock
 	down the Intel Management Engine (ME) registers. This allows U-Boot to

env/Kconfig

@@ -662,6 +662,18 @@ config SYS_MMC_ENV_PART
 	  partition 0 or the first boot partition, which is 1 or some other defined
 	  partition.
 
+config USE_ENV_MMC_PARTITION
+	bool "use the mmc environment partition name"
+	depends on ENV_IS_IN_MMC
+
+config ENV_MMC_PARTITION
+	string "mmc environment partition name"
+	depends on USE_ENV_MMC_PARTITION
+	help
+	  MMC partition name used to save environment variables.
+	  If this variable is unset, u-boot will try to get the env partition name
+	  from the device-tree's /config node.
+
 config ENV_MMC_USE_DT
 	bool "Read partition name and offset in DT"
 	depends on ENV_IS_IN_MMC && OF_CONTROL

env/mmc.c

@@ -114,8 +114,13 @@ static inline s64 mmc_offset(struct mmc *mmc, int copy)
 	if (IS_ENABLED(CONFIG_SYS_MMC_ENV_PART))
 		hwpart = mmc_get_env_part(mmc);
 
+#if defined(CONFIG_ENV_MMC_PARTITION)
+	str = CONFIG_ENV_MMC_PARTITION;
+#else
 	/* look for the partition in mmc CONFIG_SYS_MMC_ENV_DEV */
 	str = ofnode_conf_read_str(dt_prop.partition);
+#endif
+
 	if (str) {
 		/* try to place the environment at end of the partition */
 		err = mmc_offset_try_partition(str, copy, &val);