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

[Bitterblue Smith]

On 11/05/2026 19:08, Devin Wittmayer wrote:
> From: Bitterblue Smith <rtl8821cerfe2@xxxxxxxxx>
> 
> The Realtek wifi 6/7 devices which support USB 3 are weird: when first
> plugged in, they pretend to be USB 2. The driver needs to send some
> commands to the device, which make it disappear and come back as a
> USB 3 device.
> 
> Implement the required commands in rtw89.
> 
> When a USB 3 device is plugged into a USB 2 port, rtw89 will try to
> switch it to USB 3 mode only once. The device will disappear and come
> back still in USB 2 mode, of course.
> 
> Some people experience heavy interference in the 2.4 GHz band in
> USB 3 mode, so add a module parameter switch_usb_mode with the
> default value 1 to let people disable the switching.
> 
> Tested with RTL8832BU and RTL8832CU.
> 
> Signed-off-by: Bitterblue Smith <rtl8821cerfe2@xxxxxxxxx>
> Signed-off-by: Devin Wittmayer <lucid_duck@xxxxxxxxxxxxx>
> Tested-by: Devin Wittmayer <lucid_duck@xxxxxxxxxxxxx>

Are you quite sure you tested this?

> ---
>  drivers/net/wireless/realtek/rtw89/reg.h |  4 +++
>  drivers/net/wireless/realtek/rtw89/usb.c | 41 ++++++++++++++++++++++++
>  2 files changed, 45 insertions(+)
> 
> diff --git a/drivers/net/wireless/realtek/rtw89/reg.h b/drivers/net/wireless/realtek/rtw89/reg.h
> index 42ffe83931a3..7d4c085d9fb2 100644
> --- a/drivers/net/wireless/realtek/rtw89/reg.h
> +++ b/drivers/net/wireless/realtek/rtw89/reg.h
> @@ -164,6 +164,10 @@
>  #define R_AX_DBG_PORT_SEL 0x00C0
>  #define B_AX_DEBUG_ST_MASK GENMASK(31, 0)
>  
> +#define R_AX_PAD_CTRL2 0x00C4
> +#define U2SWITCHU3 0xB
> +#define USB_SWITCH_DELAY 0xF
> +
>  #define R_AX_PMC_DBG_CTRL2 0x00CC
>  #define B_AX_SYSON_DIS_PMCR_AX_WRMSK BIT(2)
>  
> diff --git a/drivers/net/wireless/realtek/rtw89/usb.c b/drivers/net/wireless/realtek/rtw89/usb.c
> index 767a95f759b1..4fb25791d118 100644
> --- a/drivers/net/wireless/realtek/rtw89/usb.c
> +++ b/drivers/net/wireless/realtek/rtw89/usb.c
> @@ -9,6 +9,11 @@
>  #include "txrx.h"
>  #include "usb.h"
>  
> +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)");
> +
>  static void rtw89_usb_read_port_complete(struct urb *urb);
>  
>  static void rtw89_usb_vendorreq(struct rtw89_dev *rtwdev, u32 addr,
> @@ -1027,6 +1032,35 @@ static void rtw89_usb_intf_deinit(struct rtw89_dev *rtwdev,
>  	usb_set_intfdata(intf, NULL);
>  }
>  
> +static int rtw89_usb_switch_mode(struct rtw89_dev *rtwdev)
> +{
> +	struct rtw89_usb *rtwusb = rtw89_usb_priv(rtwdev);
> +
> +	if (!rtw89_switch_usb_mode)
> +		return 0;
> +
> +	/* No known USB 3 devices with this chip. */
> +	if (rtwdev->chip->chip_id == RTL8851B)
> +		return 0;
> +
> +	if (rtwusb->udev->speed == USB_SPEED_SUPER)
> +		return 0;
> +
> +	rtw89_debug(rtwdev, RTW89_DBG_HCI, "%s: pad_ctrl2: %#x %#x\n",
> +		    __func__,
> +		    rtw89_read8(rtwdev, R_AX_PAD_CTRL2 + 1),
> +		    rtw89_read8(rtwdev, R_AX_PAD_CTRL2 + 2));
> +
> +	/* Already tried to switch but it's a USB 2 port. */
> +	if (rtw89_read8(rtwdev, R_AX_PAD_CTRL2 + 1) == USB_SWITCH_DELAY)
> +		return 0;
> +
> +	rtw89_write8(rtwdev, R_AX_PAD_CTRL2 + 1, USB_SWITCH_DELAY);
> +	rtw89_write8(rtwdev, R_AX_PAD_CTRL2 + 2, U2SWITCHU3);
> +
> +	return 1;
> +}
> +
>  int rtw89_usb_probe(struct usb_interface *intf,
>  		    const struct usb_device_id *id)
>  {
> @@ -1059,6 +1093,13 @@ int rtw89_usb_probe(struct usb_interface *intf,
>  		goto err_free_hw;
>  	}
>  
> +	ret = rtw89_usb_switch_mode(rtwdev);
> +	if (ret) {
> +		/* Not a fail, but we do need to skip rtw89_core_register. */
> +		ret = 0;
> +		goto err_intf_deinit;
> +	}
> +
>  	if (rtwusb->udev->speed == USB_SPEED_SUPER)
>  		rtwdev->hci.dle_type = RTW89_HCI_DLE_TYPE_USB3;
>  	else