[PATCH 4/4] mmc: core: hold SD Clock before CMD11 during Signal

[Ulf Hansson]

On 21 November 2014 at 01:51, Vincent Yang
<vincent.yang.fujitsu at gmail.com> wrote:
> Voltage Switch Procedure
>
> This patch is to fix an issue found on mb86s7x platforms.
>
> [symptom]
> There are some UHS-1 SD memory cards sometimes cannot be detected correctly,
> e.g., Transcend 600x SDXC 64GB UHS-1 memory card.
> During Signal Voltage Switch Procedure, failure to switch is indicated
> by the card holding DAT[3:0] low.
>
> [analysis]
> According to SD Host Controller Simplified Specification Version 3.00
> chapter 3.6.1, the Signal Voltage Switch Procedure should be:
> (1) Check S18A; (2) Issue CMD11; (3) Check CMD 11 response;
> (4) Stop providing SD clock; (5) Check DAT[3:0] should be 0000b;
> (6) Set 1.8V Signal Enable; (7) Wait 5ms; (8) Check 1.8V Signal Enable;
> (9) Provide SD Clock; (10) Wait 1ms; (11) Check DAT[3:0] should be 1111b;
> (12) error handling
>
> With CONFIG_MMC_CLKGATE=y, sometimes there is one more gating/un-gating
> SD clock between (2) and (3). In this case, some UHS-1 SD cards will hold
> DAT[3:0] 0000b at (11) and thus fails Signal Voltage Switch Procedure.
>
> [solution]
> By mmc_host_clk_hold() before CMD11, the additional gating/un-gating
> SD clock between (2) and (3) can be prevented and thus no failure at (11).
> It has been verified with many UHS-1 SD cards on mb86s7x platforms and
> works correctly.
>
> Signed-off-by: Vincent Yang <Vincent.Yang at tw.fujitsu.com>

Thanks! Applied for next.

Kind regards
Uffe

> ---
>  drivers/mmc/core/core.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
> index f26a5f1..8b9e2cfd 100644
> --- a/drivers/mmc/core/core.c
> +++ b/drivers/mmc/core/core.c
> @@ -1420,18 +1420,20 @@ int mmc_set_signal_voltage(struct mmc_host *host, int signal_voltage, u32 ocr)
>                 pr_warn("%s: cannot verify signal voltage switch\n",
>                         mmc_hostname(host));
>
> +       mmc_host_clk_hold(host);
> +
>         cmd.opcode = SD_SWITCH_VOLTAGE;
>         cmd.arg = 0;
>         cmd.flags = MMC_RSP_R1 | MMC_CMD_AC;
>
>         err = mmc_wait_for_cmd(host, &cmd, 0);
>         if (err)
> -               return err;
> -
> -       if (!mmc_host_is_spi(host) && (cmd.resp[0] & R1_ERROR))
> -               return -EIO;
> +               goto err_command;
>
> -       mmc_host_clk_hold(host);
> +       if (!mmc_host_is_spi(host) && (cmd.resp[0] & R1_ERROR)) {
> +               err = -EIO;
> +               goto err_command;
> +       }
>         /*
>          * The card should drive cmd and dat[0:3] low immediately
>          * after the response of cmd11, but wait 1 ms to be sure
> @@ -1480,6 +1482,7 @@ power_cycle:
>                 mmc_power_cycle(host, ocr);
>         }
>
> +err_command:
>         mmc_host_clk_release(host);
>
>         return err;
> --
> 1.9.0
>