[PATCH v3 1/2] wifi: mwifiex: ignore ROM regulatory hint on WRT3200ACM/WRT32x

[Georgi Valkov <gvalkov@gmail.com>]

WRT3200ACM and WRT32x routers always report a fixed US regulatory domain
from the mwifiex ROM, which conflicts with the platform regulatory
configuration on units sold outside the US market. For example:
- phy0 mwlwifi 5 GHz, hard-coded region 98 EU mapped to FR
- phy1 mwlwifi 2.4 GHz, hard-coded region 98 EU mapped to FR
- phy2 mwifiex 2.4 and 5 GHz, hard-coded region US

When the system boots, it detects a conflict between the user selected
region and the radios, e.g. BG FR US, and applies extreme restrictions,
preventing use of 5 GHz and DFS channels. This also affects phy0.

Implement a device-tree flag, which allows affected platforms to ignore
an incorrect regulatory hint in the ROM, so userspace can set the correct
platform regulatory domain. The radios in WRT3200ACM/WRT32x are locked to
the hard-coded configuration for which they are certified, so the only
impact is that the region conflict is avoided and the 5 GHz radios can
be used.

The change affects only platforms which explicitly define this flag, and
helps overcome the incorrect behaviour of proprietary radio firmware.

[1] https://github.com/kaloz/mwlwifi/issues/173#issuecomment-307879699
[2] https://github.com/openwrt/openwrt/issues/9956

Tested-on: WRT3200ACM, OpenWrt
Cc: stable@vger.kernel.org
Signed-off-by: Georgi Valkov <gvalkov@gmail.com>
---
Hi Jeff,
I did not consider the idea suggested by openwrt-ai, because I do not
understand it and I do not know how to implement it.
Any help is welcome!

v3:
I implemented and tested a better approach with no board specific code:
1. check for a device-tree flag in mwifiex_register_cfg80211in()
  !of_property_read_bool(of_root, "marvell,ignore-regulatory-hint")
2. add this flag to the root device tree of each affected board
Currently this affects only armada-385-linksys-rango.dts,
because Linux has no dts for venom. OpenWrt will take care of that.
This approach is more flexible and scalable, because the flag can
also be used in other drivers, e.g. mwlwifi (not part of Linux).

v2:
Replace the compatible device names, which are currently only available on
OpenWrt with board names which are available on both Linux and OpenWrt.

 drivers/net/wireless/marvell/mwifiex/cfg80211.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/net/wireless/marvell/mwifiex/cfg80211.c b/drivers/net/wireless/marvell/mwifiex/cfg80211.c
index abc703441c5d..0239b1c9214b 100644
--- a/drivers/net/wireless/marvell/mwifiex/cfg80211.c
+++ b/drivers/net/wireless/marvell/mwifiex/cfg80211.c
@@ -4899,7 +4899,14 @@ int mwifiex_register_cfg80211(struct mwifiex_adapter *adapter)
 				country_code =
 					mwifiex_11d_code_2_region(
 						adapter->region_code);
+
+				/* Allow platforms to ignore an incorrect
+				 * regulatory hint from ROM, so userspace
+				 * can set the correct regulatory domain.
+				 */
 				if (country_code &&
+				    !of_property_read_bool(of_root,
+							   "marvell,ignore-regulatory-hint") &&
 				    regulatory_hint(wiphy, country_code))
 					mwifiex_dbg(priv->adapter, ERROR,
 						    "regulatory_hint() failed\n");
-- 
2.55.0