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

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Date:   Wed, 5 Aug 2020 13:52:02 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     Adrian Hunter <adrian.hunter@...el.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

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.

Thanks,
Faiz