[PATCH v2] mmc: sdhci_am654: Add workaround for card detect debounce timer

[Ulf Hansson]

On Tue, 25 Aug 2020 at 19:00, Faiz Abbas <faiz_abbas at ti.com> wrote:
>
> There is a one time delay because of a card detect debounce timer in the
> controller IP. This timer runs as soon as power is applied to the module
> regardless of whether a card is present or not and any writes to
> SDHCI_POWER_ON will return 0 before it expires. This timeout has been
> measured to be about 1 second in am654x and j721e.
>
> Write-and-read-back in a loop on SDHCI_POWER_ON for a maximum of
> 1.5 seconds to make sure that the controller actually powers on.
>
> Signed-off-by: Faiz Abbas <faiz_abbas at ti.com>

Applied for next, thanks!

Kind regards
Uffe


> ---
>
> v2: Use read_poll_timeout() standard macro
>
>  drivers/mmc/host/sdhci_am654.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/drivers/mmc/host/sdhci_am654.c b/drivers/mmc/host/sdhci_am654.c
> index f9d24af12396..9a048c80dad4 100644
> --- a/drivers/mmc/host/sdhci_am654.c
> +++ b/drivers/mmc/host/sdhci_am654.c
> @@ -6,6 +6,7 @@
>   *
>   */
>  #include <linux/clk.h>
> +#include <linux/iopoll.h>
>  #include <linux/of.h>
>  #include <linux/module.h>
>  #include <linux/pm_runtime.h>
> @@ -272,9 +273,19 @@ static void sdhci_j721e_4bit_set_clock(struct sdhci_host *host,
>         sdhci_set_clock(host, clock);
>  }
>
> +static u8 sdhci_am654_write_power_on(struct sdhci_host *host, u8 val, int reg)
> +{
> +       writeb(val, host->ioaddr + reg);
> +       usleep_range(1000, 10000);
> +       return readb(host->ioaddr + reg);
> +}
> +
> +#define MAX_POWER_ON_TIMEOUT   1500000 /* us */
>  static void sdhci_am654_write_b(struct sdhci_host *host, u8 val, int reg)
>  {
>         unsigned char timing = host->mmc->ios.timing;
> +       u8 pwr;
> +       int ret;
>
>         if (reg == SDHCI_HOST_CONTROL) {
>                 switch (timing) {
> @@ -291,6 +302,19 @@ static void sdhci_am654_write_b(struct sdhci_host *host, u8 val, int reg)
>         }
>
>         writeb(val, host->ioaddr + reg);
> +       if (reg == SDHCI_POWER_CONTROL && (val & SDHCI_POWER_ON)) {
> +               /*
> +                * Power on will not happen until the card detect debounce
> +                * timer expires. Wait at least 1.5 seconds for the power on
> +                * bit to be set
> +                */
> +               ret = read_poll_timeout(sdhci_am654_write_power_on, pwr,
> +                                       pwr & SDHCI_POWER_ON, 0,
> +                                       MAX_POWER_ON_TIMEOUT, false, host, val,
> +                                       reg);
> +               if (ret)
> +                       dev_warn(mmc_dev(host->mmc), "Power on failed\n");
> +       }
>  }
>
>  static int sdhci_am654_execute_tuning(struct mmc_host *mmc, u32 opcode)
> --
> 2.17.1
>