RE: [PATCH rtw-next v2] wifi: rtw88: usb: do not log transfers lost to a mode switch

[Ping-Ke Shih <pkshih@realtek.com>]

Mehmet Fide <mehmet.fide@gmail.com> wrote:
> An RTL8822BU or RTL8822CU is asked to come back as a USB 3 device by
> rtw_usb_switch_mode_new(). The chip powers off its MAC and leaves the bus
> while the last control transfers of that sequence are still in flight, so
> they complete with -EPROTO and the driver reports them as errors:
> 
>   rtw_8822bu 1-1:1.0: Firmware version 27.2.0, H2C version 13
>   rtw_8822bu 1-1:1.0: write register 0xc4 failed with -71
>   usb 1-1: USB disconnect, device number 2
>   usbcore: registered new interface driver rtw_8822bu
>   rtw_8822bu 1-1:1.0: Firmware version 27.2.0, H2C version 13
> 
> Register 0xc4 is REG_PAD_CTRL2 and the access losing the race is the
> rtw_write32_set() that ends the switch sequence, a few milliseconds before
> the disconnect. Which transfer gets caught varies from boot to boot: 0xc4
> is in the "always on" section, so every write to it is followed by a second
> one from rtw_usb_reg_sec(), and sometimes that is the one that fails:
> 
>   rtw_8822bu 1-1:1.0: rtw_usb_reg_sec: reg 0x4e0, usb write 1 fail, status: -71

How about changing to use WARN_ONCE()?

[...]

> @@ -1098,6 +1098,7 @@ static int rtw_usb_switch_mode_old(struct rtw_dev *rtwdev)
>                         rtw_write8(rtwdev, REG_ACLK_MON, 0x1);
>                         rtw_write8(rtwdev, 0x3d, 0x3);
>                         /* usb disconnect */
> +                       rtwusb->switching_mode = true;
>                         rtw_write8(rtwdev, REG_SYS_PW_CTRL + 1, 0x80);
>                         return 1;
>                 }

[...]

> @@ -1151,6 +1153,11 @@ static int rtw_usb_switch_mode_new(struct rtw_dev *rtwdev)
>         rtw_write32(rtwdev, REG_PAD_CTRL2, pad_ctrl2);
>         rtw_write8(rtwdev, REG_PAD_CTRL2 + 1, 4);
> 
> +       /* From here the chip powers off its MAC and re-enumerates, so it can
> +        * leave the bus while a control transfer is still in flight.
> +        */
> +       rtwusb->switching_mode = true;
> +
>         rtw_write16_set(rtwdev, REG_SYS_PW_CTRL, BIT_APFM_OFFMAC);
>         usleep_range(1000, 1001);
>         rtw_write32_set(rtwdev, REG_PAD_CTRL2, BIT_NO_PDN_CHIPOFF_V1);

If WARN_ONCE isn't suitable, move these two assignments to caller.
I think only set `rtwusb->switching_mode = true` only if the return
value is 1.