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

From: Adrian Hunter <adrian.hunter@intel.com>
To: Faiz Abbas <faiz_abbas@ti.com>,
	linux-kernel@vger.kernel.org, linux-mmc@vger.kernel.org
Cc: ulf.hansson@linaro.org
Subject: Re: [PATCH] mmc: sdhci_am654: Add workaround for card detect debounce timer
Date: Wed, 5 Aug 2020 11:14:32 +0300	[thread overview]
Message-ID: <2d692a90-0e58-ae69-9b5b-c9eb3ffe21ec@intel.com> (raw)
In-Reply-To: <20200729234130.25056-1-faiz_abbas@ti.com>

On 30/07/20 2:41 am, Faiz Abbas 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@ti.com>
> ---
>  drivers/mmc/host/sdhci_am654.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/mmc/host/sdhci_am654.c b/drivers/mmc/host/sdhci_am654.c
> index 1718b9e8af63..55cff9de2f3e 100644
> --- a/drivers/mmc/host/sdhci_am654.c
> +++ b/drivers/mmc/host/sdhci_am654.c
> @@ -272,6 +272,7 @@ static void sdhci_j721e_4bit_set_clock(struct sdhci_host *host,
>  	sdhci_set_clock(host, clock);
>  }
>  
> +#define MAX_POWER_ON_TIMEOUT	1500 /* ms */
>  static void sdhci_am654_write_b(struct sdhci_host *host, u8 val, int reg)
>  {
>  	unsigned char timing = host->mmc->ios.timing;
> @@ -291,6 +292,26 @@ 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
> +		 */

Can you use readb_poll_timeout() here?

> +		ktime_t timeout = ktime_add_ms(ktime_get(),
> +					       MAX_POWER_ON_TIMEOUT);
> +		do {
> +			if (ktime_compare(ktime_get(), timeout) > 0) {
> +				dev_warn(mmc_dev(host->mmc),
> +					 "Power on failed\n");
> +
> +				return;
> +			}
> +
> +			writeb(val, host->ioaddr + reg);
> +			usleep_range(1000, 10000);
> +		} while (!(readb(host->ioaddr + reg) & SDHCI_POWER_ON));
> +	}
>  }
>  
>  static int sdhci_am654_execute_tuning(struct mmc_host *mmc, u32 opcode)
> 