linux-kernel - Re: [PATCH 1/2] mmc: sdhci

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Message-ID: <f27dba79-02cf-4549-87b0-464126abbe1d@ti.com>
Date: Wed, 21 Aug 2024 09:14:34 -0500
From: Judith Mendez <jm@...com>
To: Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson
	<ulf.hansson@...aro.org>
CC: <linux-mmc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mmc: sdhci_am654: Add retry tuning

Hi Adrian,

On 8/21/24 12:37 AM, Adrian Hunter wrote:
> On 15/08/24 23:15, Judith Mendez wrote:
>> Add retry tuning up to 10 times if we fail to find
>> a failing region or no passing itapdly. This is
>> necessary since some eMMC's have been observed to never
>> find a failing itapdly on the first couple of tuning
>> iterations, but eventually do. It been observed that the
>> tuning algorithm does not need to loop more than 10 times
>> before finding a failing itapdly.
>>
>> Signed-off-by: Judith Mendez <jm@...com>
>> ---
>>   drivers/mmc/host/sdhci_am654.c | 30 +++++++++++++++++++++++-------
>>   1 file changed, 23 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/mmc/host/sdhci_am654.c b/drivers/mmc/host/sdhci_am654.c
>> index 64e10f7c9faa3..c3d485bd4d553 100644
>> --- a/drivers/mmc/host/sdhci_am654.c
>> +++ b/drivers/mmc/host/sdhci_am654.c
>> @@ -86,6 +86,7 @@
>>   
>>   #define CLOCK_TOO_SLOW_HZ	50000000
>>   #define SDHCI_AM654_AUTOSUSPEND_DELAY	-1
>> +#define RETRY_TUNING_MAX	10
>>   
>>   /* Command Queue Host Controller Interface Base address */
>>   #define SDHCI_AM654_CQE_BASE_ADDR 0x200
>> @@ -151,6 +152,7 @@ struct sdhci_am654_data {
>>   	u32 flags;
>>   	u32 quirks;
>>   	bool dll_enable;
>> +	u32 tuning_loop;
>>   
>>   #define SDHCI_AM654_QUIRK_FORCE_CDTEST BIT(0)
>>   };
>> @@ -453,12 +455,14 @@ static u32 sdhci_am654_calculate_itap(struct sdhci_host *host, struct window
>>   	int prev_fail_end = -1;
>>   	u8 i;
>>   
>> -	if (!num_fails)
>> -		return ITAPDLY_LAST_INDEX >> 1;
>> +	if (!num_fails) {
>> +		/* Retry tuning */
>> +		return -1;
>> +	}
>>   
>>   	if (fail_window->length == ITAPDLY_LENGTH) {
>> -		dev_err(dev, "No passing ITAPDLY, return 0\n");
>> -		return 0;
>> +		/* Retry tuning */
>> +		return -1;
>>   	}
>>   
>>   	first_fail_start = fail_window->start;
>> @@ -504,6 +508,7 @@ static int sdhci_am654_platform_execute_tuning(struct sdhci_host *host,
>>   	u8 curr_pass, itap;
>>   	u8 fail_index = 0;
>>   	u8 prev_pass = 1;
>> +	int ret;
>>   
>>   	memset(fail_window, 0, sizeof(fail_window));
>>   
>> @@ -532,10 +537,20 @@ static int sdhci_am654_platform_execute_tuning(struct sdhci_host *host,
>>   	if (fail_window[fail_index].length != 0)
>>   		fail_index++;
>>   
>> -	itap = sdhci_am654_calculate_itap(host, fail_window, fail_index,
>> -					  sdhci_am654->dll_enable);
>> +	ret = sdhci_am654_calculate_itap(host, fail_window, fail_index,
>> +					 sdhci_am654->dll_enable);
>>   
>> -	sdhci_am654_write_itapdly(sdhci_am654, itap, sdhci_am654->itap_del_ena[timing]);
>> +	if (ret >= 0) {
>> +		itap = ret;
>> +		sdhci_am654_write_itapdly(sdhci_am654, itap, sdhci_am654->itap_del_ena[timing]);
>> +	} else {
>> +		if (sdhci_am654->tuning_loop < RETRY_TUNING_MAX) {
>> +			sdhci_am654->tuning_loop++;
>> +			sdhci_am654_platform_execute_tuning(host, opcode);
> 
> The kernel uses very small stack size, so recursive function calls
> should not be used.  It would be better to put the loop in a separate
> function, or add a retry: label and goto retry.

Ok, can change to this method, I was not sure of recursive function
call but had opted for that since the code was to be simpler.

> 
>> +		} else {
>> +			return -1;
>> +		}
>> +	}
>>   
>>   	/* Save ITAPDLY */
>>   	sdhci_am654->itap_del_sel[timing] = itap;
>> @@ -908,6 +923,7 @@ static int sdhci_am654_probe(struct platform_device *pdev)
>>   		goto err_pltfm_free;
>>   	}
>>   
>> +	sdhci_am654->tuning_loop = 0;
> 
> So this is 10 retries ever, since sdhci_am654->tuning_loop is never
> set back to 0.  Is that the intention?

Yes, maximum of 10 re-tries. So far we have only seen issues during
boot.

~ Judith

> 
>>   	host->mmc_host_ops.execute_tuning = sdhci_am654_execute_tuning;
>>   
>>   	pm_runtime_get_noresume(dev);
>