Re: [PATCH] wifi: rtw88: fix race condition when doing H2C command

[Sascha Hauer <sha@pengutronix.de>]

On Thu, Nov 24, 2022 at 02:44:42PM +0800, Ping-Ke Shih wrote:
> From: Ji-Pin Jou <neo_jou@realtek.com>
> 
> For SDIO/USB interface, since the tranferring speed is slower than
> that in PCIE, it may have race condition when the driver sets down
> H2C command to the FW.
> 
> In the function rtw_fw_send_h2c_command, before the patch, box_reg
> is written first, then box_ex_reg is written. FW starts to work and
> fetch the value of box_ex_reg,  when the most significant byte of
> box_reg(4 bytes) is written. Meanwhile, for SDIO/USB interface,
> since the transferring speed is slow, the driver is still in writing
> the new value of box_ex_reg through the bus, and FW may get the
> wrong value of box_ex_reg at the moment.
> 
> To prevent the above driver/FW racing situation, box_ex_reg is
> written first then box_reg. Furthermore, it is written in 4 bytes at
> a time, instead of written in one byte one by one. It can increase
> the speed for SDIO/USB interface.
> 
> Signed-off-by: Ji-Pin Jou <neo_jou@realtek.com>
> Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>

This solves the issue with the RTW88 USB patch set reported here:

https://lore.kernel.org/linux-wireless/20221122145527.GA29978@pengutronix.de/

Tested-by: Sascha Hauer <s.hauer@pengutronix.de>

Sascha

> ---
>  drivers/net/wireless/realtek/rtw88/fw.c | 8 +++-----
>  drivers/net/wireless/realtek/rtw88/fw.h | 5 +++++
>  2 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/wireless/realtek/rtw88/fw.c b/drivers/net/wireless/realtek/rtw88/fw.c
> index 0b5f903c0f366..b290811d75e1c 100644
> --- a/drivers/net/wireless/realtek/rtw88/fw.c
> +++ b/drivers/net/wireless/realtek/rtw88/fw.c
> @@ -311,10 +311,10 @@ EXPORT_SYMBOL(rtw_fw_c2h_cmd_isr);
>  static void rtw_fw_send_h2c_command(struct rtw_dev *rtwdev,
>  				    u8 *h2c)
>  {
> +	struct rtw_h2c_cmd *h2c_cmd = (struct rtw_h2c_cmd *)h2c;
>  	u8 box;
>  	u8 box_state;
>  	u32 box_reg, box_ex_reg;
> -	int idx;
>  	int ret;
>  
>  	rtw_dbg(rtwdev, RTW_DBG_FW,
> @@ -356,10 +356,8 @@ static void rtw_fw_send_h2c_command(struct rtw_dev *rtwdev,
>  		goto out;
>  	}
>  
> -	for (idx = 0; idx < 4; idx++)
> -		rtw_write8(rtwdev, box_reg + idx, h2c[idx]);
> -	for (idx = 0; idx < 4; idx++)
> -		rtw_write8(rtwdev, box_ex_reg + idx, h2c[idx + 4]);
> +	rtw_write32(rtwdev, box_ex_reg, le32_to_cpu(h2c_cmd->msg_ext));
> +	rtw_write32(rtwdev, box_reg, le32_to_cpu(h2c_cmd->msg));
>  
>  	if (++rtwdev->h2c.last_box_num >= 4)
>  		rtwdev->h2c.last_box_num = 0;
> diff --git a/drivers/net/wireless/realtek/rtw88/fw.h b/drivers/net/wireless/realtek/rtw88/fw.h
> index a5a965803a3cc..bca610dc99ab7 100644
> --- a/drivers/net/wireless/realtek/rtw88/fw.h
> +++ b/drivers/net/wireless/realtek/rtw88/fw.h
> @@ -81,6 +81,11 @@ struct rtw_c2h_adaptivity {
>  	u8 option;
>  } __packed;
>  
> +struct rtw_h2c_cmd {
> +	__le32 msg;
> +	__le32 msg_ext;
> +} __packed;
> +
>  enum rtw_rsvd_packet_type {
>  	RSVD_BEACON,
>  	RSVD_DUMMY,
> -- 
> 2.25.1
> 

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