wifi: rtw88: rtw8821c: Fix rfe_option field width

[ Upstream commit 14705f969d ]

On my RTW8821CU chipset rfe_option reads as 0x22. Looking at the
vendor driver suggests that the field width of rfe_option is 5 bit,
so rfe_option should be masked with 0x1f.

Without this the rfe_option comparisons with 2 further down the
driver evaluate as false when they should really evaluate as true.
The effect is that 2G channels do not work.

rfe_option is also used as an array index into rtw8821c_rfe_defs[].
rtw8821c_rfe_defs[34] (0x22) was added as part of adding USB support,
likely because rfe_option reads as 0x22. As this now becomes 0x2,
rtw8821c_rfe_defs[34] is no longer used and can be removed.

Note that this might not be the whole truth. In the vendor driver
there are indeed places where the unmasked rfe_option value is used.
However, the driver has several places where rfe_option is tested
with the pattern if (rfe_option == 2 || rfe_option == 0x22) or
if (rfe_option == 4 || rfe_option == 0x24), so that rfe_option BIT(5)
has no influence on the code path taken. We therefore mask BIT(5)
out from rfe_option entirely until this assumption is proved wrong
by some chip variant we do not know yet.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Alexandru gagniuc <mr.nuke.me@gmail.com>
Tested-by: Larry Finger <Larry.Finger@lwfinger.net>
Tested-by: ValdikSS <iam@valdikss.org.ru>
Cc: stable@vger.kernel.org
Reviewed-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230417140358.2240429-3-s.hauer@pengutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/net/wireless/realtek/rtw88/rtw8821c.c

@@ -40,7 +40,7 @@ static int rtw8821c_read_efuse(struct rtw_dev *rtwdev, u8 *log_map)
 
 	map = (struct rtw8821c_efuse *)log_map;
 
-	efuse->rfe_option = map->rfe_option;
+	efuse->rfe_option = map->rfe_option & 0x1f;
 	efuse->rf_board_option = map->rf_board_option;
 	efuse->crystal_cap = map->xtal_k;
 	efuse->pa_type_2g = map->pa_type;