RE: [PATCH rtw-next v4] wifi: rtw88: usb: do not log transfers lost to a mode switch

Mehmet Fide <[email protected]> wrote:
> From: Mehmet Fide <[email protected]>
> 
> 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
> 
> Nothing is wrong here. The device re-enumerates, probes again and registers
> normally, which is why rtw_usb_probe() already treats a non-zero return
> from rtw_usb_switch_mode() as "Not a fail". On a USB 2 only port the
> switch can never succeed, so the message returns on every boot and
> everyone using such a port has to work out that it is harmless.
> 
> Mark the window in which the chip is expected to leave the bus and skip the
> error reports for transfers that fall into it. The mark is a rtw_flags bit
> set in rtw_usb_switch_mode(), so it covers both the new and the old switch
> sequence, and it is cleared again right after them: the transfers that lose
> the race are issued from inside the sequences, and anything that fails
> later must be reported again.
> 
> Tested with an RTL8822BU (0x7392:0xb822) on a USB 2 root port of a TI AM62,
> where the message appears exactly once per boot. With the patch both lines
> are gone while the disconnect, the re-enumeration and the second firmware
> load are unchanged.
> 
> Signed-off-by: Mehmet Fide <[email protected]>
> ---
> v4:
>  - track the window with a RTW_FLAG_SWITCHING_USB_MODE bit in rtw_flags
>    instead of a bool in struct rtw_usb, clear it unconditionally right
>    after the switch sequences so later failures are reported again, and
>    drop the comment block in usb.c (Ping-Ke Shih)
>  - Signed-off-by switched to my work address to match my other patches
> v3:
>  - set the mark in rtw_usb_switch_mode() instead of in the two switch
>    helpers (Ping-Ke Shih)
> 
>  drivers/net/wireless/realtek/rtw88/main.h |  2 ++
>  drivers/net/wireless/realtek/rtw88/usb.c  | 22 +++++++++++++++++-----
>  2 files changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/wireless/realtek/rtw88/main.h b/drivers/net/wireless/realtek/rtw88/main.h
> index c6e981ba7..fc3fb617c 100644
> --- a/drivers/net/wireless/realtek/rtw88/main.h
> +++ b/drivers/net/wireless/realtek/rtw88/main.h
> @@ -377,6 +377,8 @@ enum rtw_flags {
>         RTW_FLAG_RESTARTING,
>         RTW_FLAG_RESTART_TRIGGERING,
>         RTW_FLAG_FORCE_LOWEST_RATE,
> +       /* USB mode switch: the chip re-enumerates, transfers may be cut off */

As we didn't add comments for existing enumerators, add the comment in USB code
if you actually need this. (I think no need though)

> +       RTW_FLAG_SWITCHING_USB_MODE,
> 
>         NUM_OF_RTW_FLAGS,
>  };