Re: [PATCH 1/2] mmc: sdhci_am654: Add retry tuning

[Judith Mendez <jm@xxxxxx>]

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@xxxxxx>
> > ---
> >   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);