generic: platform/mikrotik: add wlan lz77 decompress

A number of new (or with recently updated caldata)
Mikrotik devices are using LZ77 magic for wlan tag hard_config data.
New devices include the Chateau LTE12 [1], and ax devices [2]
Newly factory flashed devices may include the hap ac3 [3]

This can be seen in decoded OEM supout [4] dmesg:
"radio data lz77 decompressed from"…

Investigating an arm RouterOS flash.ko module, and supplied example
hard_config dumps, the format was guessed via decompilation and live
debugging [5]. This decoder was then built from the guessed format
specification.

debug prints can be enabled in a DYNAMIC_DEBUG kernel build via the
kernel cmdline:

        chosen {
-               bootargs = "console=ttyS0,115200";
+               bootargs = "console=ttyS0,115200 dyndbg=\"file drivers/platform/mikrotik/* +p\"";
        };

[1]: https://forum.openwrt.org/t/no-wireless-mikrotik-rbd53ig-5hacd2hnd/157763/4
[2]: https://forum.openwrt.org/t/mikrotik-routeros-v7-x-and-openwrt-sysupgrade/148072/17
[3]: https://forum.openwrt.org/t/adding-support-for-mikrotik-hap-ax2/133715/47
[4]: https://github.com/farseeker/go-mikrotik-rif
[5]: https://github.com/john-tho/routeros-wlan-lz77-decode

Signed-off-by: John Thomson <[email protected]>

target/linux/ath79/mikrotik/config-default

@@ -15,6 +15,7 @@ CONFIG_MFD_CORE=y
 CONFIG_MFD_RB4XX_CPLD=y
 CONFIG_MIKROTIK=y
 CONFIG_MIKROTIK_RB_SYSFS=y
+CONFIG_MIKROTIK_WLAN_DECOMPRESS_LZ77=y
 CONFIG_MTD_NAND_AR934X=y
 CONFIG_MTD_NAND_CORE=y
 CONFIG_MTD_NAND_ECC=y

target/linux/generic/files/drivers/platform/mikrotik/Kconfig

@@ -21,4 +21,11 @@ config NVMEM_LAYOUT_MIKROTIK
 	help
 	  This driver exposes MikroTik hard_config via NVMEM layout.
 
+config MIKROTIK_WLAN_DECOMPRESS_LZ77
+	tristate "Mikrotik factory Wi-Fi caldata LZ77 decompression support"
+	depends on MIKROTIK_RB_SYSFS
+	help
+	  Allow Mikrotik LZ77 factory flashed Wi-Fi calibration data to be
+	  decompressed
+
 endif # MIKROTIK

target/linux/generic/files/drivers/platform/mikrotik/Makefile

@@ -3,3 +3,4 @@
 #
 obj-$(CONFIG_MIKROTIK_RB_SYSFS)     += routerboot.o rb_hardconfig.o rb_softconfig.o
 obj-$(CONFIG_NVMEM_LAYOUT_MIKROTIK)     += rb_nvmem.o
+obj-$(CONFIG_MIKROTIK_WLAN_DECOMPRESS_LZ77)  += mikrotik_wlan_lz77.o