linux-kernel - Re: [PATCH wireless v1] wifi: rtw88: sdio: Always use two consecutive bytes for word operations

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Date:   Mon, 15 May 2023 22:18:41 +1000
From:   Julian Calaby <julian.calaby@...il.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
        pkshih@...ltek.com, tony0620emma@...il.com, kvalo@...nel.org,
        Larry Finger <Larry.Finger@...inger.net>,
        Rudi Heitbaum <rudi@...tbaum.com>, linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH wireless v1] wifi: rtw88: sdio: Always use two consecutive
 bytes for word operations

Hi Martin,

On Mon, May 15, 2023 at 6:12 AM Martin Blumenstingl
<martin.blumenstingl@...glemail.com> wrote:
>
> The Allwinner sunxi-mmc controller cannot handle word (16 bit)
> transfers. So and sdio_{read,write}w fails with messages like the
> following example using an RTL8822BS (but the same problems were also
> observed with RTL8822CS and RTL8723DS chips):
>   rtw_8822bs mmc1:0001:1: Firmware version 27.2.0, H2C version 13
>   sunxi-mmc 4021000.mmc: unaligned scatterlist: os f80 length 2
>   sunxi-mmc 4021000.mmc: map DMA failed
>   rtw_8822bs mmc1:0001:1: sdio read16 failed (0x10230): -22
>
> Use two consecutive single byte accesses for word operations instead. It
> turns out that upon closer inspection this is also what the vendor
> driver does, even though it does have support for sdio_{read,write}w. So
> we can conclude that the rtw88 chips do support word access but only on
> SDIO controllers that also support it. Since there's no way to detect if
> the controller supports word access or not the rtw88 sdio driver
> switches to the easiest approach: avoiding word access.
>
> Reported-by: Larry Finger <Larry.Finger@...inger.net>
> Closes: https://lore.kernel.org/linux-wireless/527585e5-9cdd-66ed-c3af-6da162f4b720@lwfinger.net/
> Reported-by: Rudi Heitbaum <rudi@...tbaum.com>
> Fixes: 65371a3f14e7 ("wifi: rtw88: sdio: Add HCI implementation for SDIO based chipsets")
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>

The linux-sunxi folks might have comments, so I've added them to CC.

> ---
>  drivers/net/wireless/realtek/rtw88/sdio.c | 8 --------
>  1 file changed, 8 deletions(-)
>
> diff --git a/drivers/net/wireless/realtek/rtw88/sdio.c b/drivers/net/wireless/realtek/rtw88/sdio.c
> index af0459a79899..06fce7c3adda 100644
> --- a/drivers/net/wireless/realtek/rtw88/sdio.c
> +++ b/drivers/net/wireless/realtek/rtw88/sdio.c
> @@ -87,11 +87,6 @@ static void rtw_sdio_writew(struct rtw_dev *rtwdev, u16 val, u32 addr,
>         u8 buf[2];
>         int i;
>
> -       if (rtw_sdio_use_memcpy_io(rtwdev, addr, 2)) {
> -               sdio_writew(rtwsdio->sdio_func, val, addr, err_ret);
> -               return;
> -       }
> -
>         *(__le16 *)buf = cpu_to_le16(val);
>
>         for (i = 0; i < 2; i++) {
> @@ -125,9 +120,6 @@ static u16 rtw_sdio_readw(struct rtw_dev *rtwdev, u32 addr, int *err_ret)
>         u8 buf[2];
>         int i;
>
> -       if (rtw_sdio_use_memcpy_io(rtwdev, addr, 2))
> -               return sdio_readw(rtwsdio->sdio_func, addr, err_ret);
> -
>         for (i = 0; i < 2; i++) {
>                 buf[i] = sdio_readb(rtwsdio->sdio_func, addr + i, err_ret);
>                 if (*err_ret)
> --
> 2.40.1
>

Thanks,

--
Julian Calaby

Email: julian.calaby@...il.com
Profile: http://www.google.com/profiles/julian.calaby/