linux-kernel - Re: [PATCH 2/2] mmc: sdhci_am654: Add tuning debug prints

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Message-ID: <CAPDyKFoekvs1XLGVewB8vA=rsGN4ikB9uw80AVw6NVRF-rgffA@mail.gmail.com>
Date: Tue, 20 Aug 2024 17:03:54 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Judith Mendez <jm@...com>
Cc: Adrian Hunter <adrian.hunter@...el.com>, linux-mmc@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mmc: sdhci_am654: Add tuning debug prints

On Tue, 20 Aug 2024 at 16:41, Judith Mendez <jm@...com> wrote:
>
> Hi Ulf Hansson,
>
> On 8/20/24 6:33 AM, Ulf Hansson wrote:
> > On Thu, 15 Aug 2024 at 22:15, Judith Mendez <jm@...com> wrote:
> >>
> >> Add debug prints to tuning algorithm for debugging.
> >>
> >> Signed-off-by: Judith Mendez <jm@...com>
> >> ---
> >>   drivers/mmc/host/sdhci_am654.c | 5 +++++
> >>   1 file changed, 5 insertions(+)
> >>
> >> diff --git a/drivers/mmc/host/sdhci_am654.c b/drivers/mmc/host/sdhci_am654.c
> >> index c3d485bd4d553..a909f8de0eabe 100644
> >> --- a/drivers/mmc/host/sdhci_am654.c
> >> +++ b/drivers/mmc/host/sdhci_am654.c
> >> @@ -457,11 +457,13 @@ static u32 sdhci_am654_calculate_itap(struct sdhci_host *host, struct window
> >>
> >>          if (!num_fails) {
> >>                  /* Retry tuning */
> >> +               dev_err(dev, "No failing region found, retry tuning\n");
> >
> > A dev_err seems to be too heavy, but I am not sure at what frequency
> > this could occur?
>
> Having no failing region is what we call a corner case, it rarely
> happens. The one case where it did happen, it took a good amount
> of time to discover there were no failing regions found. The tuning
> algorithm had to be looped 3 times before finding a failing itapdly.
>
> >
> > Why isn't a dev_dbg sufficient?
>
> I thought about using dev_dbg, but based on some feedback after coming
> upon this issue on a board bring up case, we think it would help
> enormously if we make it as obvious as possible when no failing region
> is found.
>
> The one case where this came up, the dev_err print would only print 3
> times... Now this is only one case and we are not aware of any more
> cases like this, also we cannot replicate on TI EVM's.

What happens if/when we fail here? Do we fail to detect the card or do
we end up running it in some degraded mode?

If the latter a dev_warn, the former a dev_err(). Does that make sense?

>
> >
> >>                  return -1;
> >>          }
> >>
> >>          if (fail_window->length == ITAPDLY_LENGTH) {
> >>                  /* Retry tuning */
> >> +               dev_err(dev, "No passing ITAPDLY, retry tuning\n");
> >
> > Ditto.
>
> Same idea as above..
>
> But with this print, the maximum amount of prints that could be printed
> is 20, is this too many prints in your opinion?

This sounds like dev_dbg to me. We are not really failing, as we are
making a re-try and will most likely succeed then, right?

>
>
> >
> >>                  return -1;
> >>          }
> >>
> >> @@ -505,6 +507,7 @@ static int sdhci_am654_platform_execute_tuning(struct sdhci_host *host,
> >>          struct sdhci_am654_data *sdhci_am654 = sdhci_pltfm_priv(pltfm_host);
> >>          unsigned char timing = host->mmc->ios.timing;
> >>          struct window fail_window[ITAPDLY_LENGTH];
> >> +       struct device *dev = mmc_dev(host->mmc);
> >>          u8 curr_pass, itap;
> >>          u8 fail_index = 0;
> >>          u8 prev_pass = 1;
> >> @@ -542,12 +545,14 @@ static int sdhci_am654_platform_execute_tuning(struct sdhci_host *host,
> >>
> >>          if (ret >= 0) {
> >>                  itap = ret;
> >> +               dev_dbg(dev, "Final ITAPDLY=%d\n", itap);
> >>                  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);
> >>                  } else {
> >> +                       dev_err(dev, "Failed to find ITAPDLY, fail tuning\n");
> >
> > The commit message only talks about debug messages, but this is an
> > error message. Perhaps update the commit message a bit?
>
> Sure will do, after we conclude the discussion above and in v2.
>
> Thanks so much for reviewing.
>

Kind regards
Uffe