RE: [PATCH rtw-next v5] wifi: rtw88: usb: Download the reserved page synchronously

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

Josef Schlehofer <pepe.schlehofer@gmail.com> wrote:
> From: Mohammed Afifi <i.mafifi17@gmail.com>
> 
> In AP mode the reserved page (which contains the beacon) is downloaded
> to the chip by rtw_fw_write_data_rsvd_page(). That function writes the
> data via rtw_hci_write_data_rsvd_page() and then immediately polls the
> hardware BCN_VALID bit to confirm the firmware accepted the beacon.
> 
> On USB, rtw_usb_write_data_rsvd_page() ends up in rtw_usb_write_port(),
> which submits the URB with usb_submit_urb() and returns as soon as the
> transfer is queued. The completion callback only frees the skb. As a
> result the BCN_VALID poll can run while the beacon is still in flight
> on the bus, and the poll times out even though the download itself is
> fine.
> 
> This shows up as:
> 
>   rtw_8822bu: error beacon valid
>   rtw_8822bu: failed to download drv rsvd page
> 
> The failure is intermittent because the poll retries sometimes cover
> the transfer time. It occurs in bursts when something triggers repeated
> beacon updates, such as stations associating and disassociating.
> 
> Fix this by making rtw_usb_write_data() wait for the URB to complete
> when it's called from rtw_usb_write_data_rsvd_page(). The new
> rtw_usb_write_port_sync() waits the same way usb_bulk_msg() does: if
> the URB doesn't complete within 5 seconds, it is killed before the
> function returns, so the completion handler can't run after that.
> usb_bulk_msg() itself is not used because it can't set URB_ZERO_PACKET,
> which rtw_usb_write_port() sets for every bulk out transfer.
> 
> Only the reserved page path is made synchronous; the normal data TX
> path and the H2C path are left untouched, so throughput is unaffected.
> The chips with a 3081 WCPU also download their firmware through
> rtw_usb_write_data_rsvd_page(), so those chunks are now sent
> synchronously as well.
> 
> The reserved page download runs in process context under rtwdev->mutex,
> so sleeping there is safe.
> 
> Closes: https://github.com/lwfinger/rtw88/issues/451
> Signed-off-by: Mohammed Afifi <i.mafifi17@gmail.com>
> Signed-off-by: Bitterblue Smith <rtl8821cerfe2@gmail.com>
> Co-developed-by: Josef Schlehofer <pepe.schlehofer@gmail.com>
> Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>

Acked-by: Ping-Ke Shih <pkshih@realtek.com>