[PATCH] mmc: meson-gx: work around broken SDIO with certain WiFi chips

[Martin Blumenstingl]

Hi Heiner,

thanks for finding a solution (it didn't even take you long)!

On Thu, Jun 8, 2017 at 8:43 PM, Heiner Kallweit <hkallweit1 at gmail.com> wrote:
> There have been reports about SDIO failing with certain WiFi chips in
> descriptor chain mode. SD / eMMC are working fine.
>
> So let's fall back to bounce buffer mode for command SD_IO_RW_EXTENDED.
> This was reported to fix this error.
>
> Fixes: 79ed05e329c3 "mmc: meson-gx: add support for descriptor chain mode"
> Cc: <stable at vger.kernel.org> # 4.12.x
> Signed-off-by: Heiner Kallweit <hkallweit1 at gmail.com>
Tested-by: Martin Blumenstingl <martin.blumenstingl at googlemail.com>

> ---
>  drivers/mmc/host/meson-gx-mmc.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/drivers/mmc/host/meson-gx-mmc.c b/drivers/mmc/host/meson-gx-mmc.c
> index 1842ed34..4cdbe3c0 100644
> --- a/drivers/mmc/host/meson-gx-mmc.c
> +++ b/drivers/mmc/host/meson-gx-mmc.c
> @@ -210,6 +210,15 @@ static void meson_mmc_get_transfer_mode(struct mmc_host *mmc,
>         int i;
>         bool use_desc_chain_mode = true;
>
> +       /*
> +        * Broken SDIO with AP6335-based WiFi on Khadas VIM Pro has been
nit-pick: Khadas VIM Pro uses an Ampak AP6255 (not AP6335)

> +        * reported. For some strange reason this occurs in descriptor
> +        * chain mode only. So let's fall back to bounce buffer mode
> +        * for command SD_IO_RW_EXTENDED.
> +        */
> +       if (mrq->cmd->opcode == SD_IO_RW_EXTENDED)
> +               return;
> +
>         for_each_sg(data->sg, sg, data->sg_len, i)
>                 /* check for 8 byte alignment */
>                 if (sg->offset & 7) {
> --
> 2.13.0
>
for the record: wireless performance with this patch applied is excellent

# iperf3 --client <server ip>
Connecting to host <server ip>, port 5201
[  4] local <khadas vim ip> port 38352 connected to <server ip> port 5201
[ ID] Interval           Transfer     Bandwidth       Retr  Cwnd
[  4]   0.00-1.00   sec  8.19 MBytes  68.7 Mbits/sec    0    349 KBytes
[  4]   1.00-2.00   sec  8.56 MBytes  71.8 Mbits/sec    1    287 KBytes
[  4]   2.00-3.00   sec  8.89 MBytes  74.6 Mbits/sec    0    315 KBytes
[  4]   3.00-4.00   sec  8.59 MBytes  72.1 Mbits/sec    0    344 KBytes
[  4]   4.00-5.00   sec  9.11 MBytes  76.5 Mbits/sec    0    355 KBytes
[  4]   5.00-6.00   sec  8.92 MBytes  74.8 Mbits/sec    0    356 KBytes
[  4]   6.00-7.00   sec  8.75 MBytes  73.4 Mbits/sec    0    356 KBytes
[  4]   7.00-8.00   sec  8.79 MBytes  73.7 Mbits/sec    0    356 KBytes
[  4]   8.00-9.00   sec  8.64 MBytes  72.5 Mbits/sec    0    359 KBytes
[  4]   9.00-10.00  sec  8.98 MBytes  75.3 Mbits/sec    0    366 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth       Retr
[  4]   0.00-10.00  sec  87.4 MBytes  73.3 Mbits/sec    1             sender
[  4]   0.00-10.00  sec  87.0 MBytes  73.0 Mbits/sec                  receiver

iperf Done.
# iperf3 --client <server ip> -R
Connecting to host <server ip>, port 5201
Reverse mode, remote host <server ip> is sending
[  4] local <khadas vim ip> port 38356 connected to <server ip> port 5201
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec  2.04 MBytes  17.1 Mbits/sec
[  4]   1.00-2.00   sec  2.17 MBytes  18.2 Mbits/sec
[  4]   2.00-3.00   sec  3.85 MBytes  32.3 Mbits/sec
[  4]   3.00-4.00   sec  7.60 MBytes  63.8 Mbits/sec
[  4]   4.00-5.00   sec  6.90 MBytes  57.9 Mbits/sec
[  4]   5.00-6.00   sec  6.46 MBytes  54.2 Mbits/sec
[  4]   6.00-7.00   sec  7.49 MBytes  62.9 Mbits/sec
[  4]   7.00-8.00   sec  7.11 MBytes  59.7 Mbits/sec
[  4]   8.00-9.00   sec  6.58 MBytes  55.2 Mbits/sec
[  4]   9.00-10.00  sec  6.83 MBytes  57.3 Mbits/sec
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bandwidth       Retr
[  4]   0.00-10.00  sec  58.8 MBytes  49.3 Mbits/sec   30             sender
[  4]   0.00-10.00  sec  57.4 MBytes  48.2 Mbits/sec                  receiver

iperf Done.