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

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Date:   Wed, 5 Aug 2020 12:46:53 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Faiz Abbas <faiz_abbas@...com>, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org
Cc:     ulf.hansson@...aro.org
Subject: Re: [PATCH] mmc: sdhci_am654: Add workaround for card detect debounce
 timer

On 5/08/20 11:22 am, Faiz Abbas wrote:
> Hi Adrian,
> 
> On 05/08/20 1:44 pm, Adrian Hunter wrote:
>> 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@...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?
>>
> 
> The loop is write -> readback -> check for set bit -> write again and so on until timeout
> so poll_timeout() calls will not work.

I mentioned it because pedantically you need to check the condition
again after a timeout.  Alternatively, the read_poll_timeout macro
can be used with a function, something like below (not even compile
tested!)

static u8 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;

	if (reg == SDHCI_HOST_CONTROL) {
		switch (timing) {
		/*
		 * According to the data manual, HISPD bit
		 * should not be set in these speed modes.
		 */
		case MMC_TIMING_SD_HS:
		case MMC_TIMING_MMC_HS:
		case MMC_TIMING_UHS_SDR12:
		case MMC_TIMING_UHS_SDR25:
			val &= ~SDHCI_CTRL_HISPD;
		}
	}

	writeb(val, host->ioaddr + reg);

	/*
	 * 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
	 */
	if (reg == SDHCI_POWER_CONTROL && (val & SDHCI_POWER_ON) &&
	    read_poll_timeout(write_power_on, pwr, (pwr & SDHCI_POWER_ON), 0,
			      MAX_POWER_ON_TIMEOUT, false, host, val, reg))
			dev_warn(mmc_dev(host->mmc), "Power on failed\n");
			return;
		}
	}
}