RE: [PATCH rtw-next v2 1/1] wifi: rtw89: usb: Support switching to USB 3 mode

[Ping-Ke Shih]

Devin Wittmayer <lucid_duck@xxxxxxxxxxxxx> wrote: 
> 
> On Mon, 2026-05-11 at 19:26 +0200, Johannes Berg wrote:
> > > +static bool rtw89_switch_usb_mode = true;
> > > +module_param_named(switch_usb_mode, rtw89_switch_usb_mode, bool, 0644);
> > > +MODULE_PARM_DESC(switch_usb_mode,
> > > +         "Set to N to disable switching to USB 3 mode to avoid potential interference in the 2.4
> GHz band (default: Y)");
> >
> > We shouldn't really add new module parameters.
 This module parameter follows the pattern Bitterblue established for
> rtw88: same user-facing name (switch_usb_mode), same description, same
> default. Commit 315c23a64e99 "wifi: rtw88: usb: Support USB 3 with
> RTL8822CU/RTL8822BU" (2024-07-10) added it to rtw88/usb.c and it
> remains in-tree.

I took the patch of rtw88 because we switch USB mode at probe stage, but
USB 3 mode has interference on 2.4GHz band (as the comment says). If a user
insist on 2.4GHz with a good performance, this is an option to keep USB 2
mode.

> 
> Three v3 paths I see:
> 
> 1. Drop the param. Users hitting USB3 2.4 GHz harmonic interference
>    would need to use a USB 2 port instead.
> 2. Move the escape hatch behind a sysfs or nl80211 control. New UABI
>    surface; open to design suggestions on that.
> 3. Keep it for rtw89/rtw88 symmetry on the same USB3 / 2.4 GHz
>    harmonic interference issue.

An additional option might be to not support 2.4GHz channels when switching
to USB 3. But I'm not really sure if it is acceptable to USB users.

Ping-Ke