Bitterblue Smith <rtl8821cerfe2@xxxxxxxxx> wrote:
> This read_poll_timeout_atomic() with a delay of 1 µs and a timeout of
> 1000000 µs can take ~250 seconds in the worst case because sending a
> USB control message takes ~250 µs.
I was not aware of the change of [1]. The behavior of atomic version becomes
different from non-atomic version.
For this patch, I feel we can keep delay_us to 1 and treat timeout_us as
'count', which USB devices do smaller retries. The smaller delay_us can
reduce total polling time, especially for PCIE devices (see my comments below)
Though I don't measure total polling time of patch 2/2, I feel we can apply
similar idea.
[1] 7349a69cf312 ("iopoll: Do not use timekeeping in read_poll_timeout_atomic()")
>
> Increase the delay to 250 µs in order to reduce the maximum polling
> time to ~2 seconds.
>
> This problem was observed with RTL8851BU while suspending to RAM with
> WOWLAN enabled. The computer sat for 4 minutes with a black screen
> before suspending.
>
> Signed-off-by: Bitterblue Smith <rtl8821cerfe2@xxxxxxxxx>
> ---
> drivers/net/wireless/realtek/rtw89/fw.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/wireless/realtek/rtw89/fw.c b/drivers/net/wireless/realtek/rtw89/fw.c
> index c613431e754f..27d84464347b 100644
> --- a/drivers/net/wireless/realtek/rtw89/fw.c
> +++ b/drivers/net/wireless/realtek/rtw89/fw.c
> @@ -6665,7 +6665,7 @@ static int rtw89_fw_read_c2h_reg(struct rtw89_dev *rtwdev,
>
> info->id = RTW89_FWCMD_C2HREG_FUNC_NULL;
>
> - ret = read_poll_timeout_atomic(rtw89_read8, val, val, 1,
> + ret = read_poll_timeout_atomic(rtw89_read8, val, val, 250,
As my experiments, PCIE devices take about 30us for this polling, when
setting delay 1. But it will take 256us, if delay is changed to 250.
I feel we need to set this value by HCI type if needed.
> RTW89_C2H_TIMEOUT, false, rtwdev,
> chip->c2h_ctrl_reg);
> if (ret) {
> --
> 2.50.0
