linux-kernel - Re: [PATCH] mmc: sdhci-sprd: Fix minimum clock limit

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Message-ID: <CA+Da2qwe96J_EyJCG04UX5GBEsoU0mckWktPyTrZARk-XHAo0w@mail.gmail.com>
Date:   Tue, 11 Oct 2022 16:40:19 +0800
From:   Wenchao Chen <wenchao.chen666@...il.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     ulf.hansson@...aro.org, orsonzhai@...il.com,
        baolin.wang@...ux.alibaba.com, zhang.lyra@...il.com,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        megoo.tang@...il.com, lzx.stg@...il.com
Subject: Re: [PATCH] mmc: sdhci-sprd: Fix minimum clock limit

On Tue, Oct 11, 2022 at 2:45 PM Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> On 11/10/22 09:30, Wenchao Chen wrote:
> > From: Wenchao Chen <wenchao.chen@...soc.com>
> >
> > The minimum clock supported by SPRD Host is 100000.
>
> Commit messages are better if they say why a change
> is being made.
>
> This begs the question, was there a problem with 400 kHz?
> Are there cases that benefit from this change?
> Should it have a fixes tag,cc stable?
>

Code show as below:
static struct sdhci_ops sdhci_sprd_ops = {
...
.get_min_clock = sdhci_sprd_get_min_clock,
...
};

int sdhci_setup_host(struct sdhci_host *host)
{
...
if (host->ops->get_min_clock)
mmc->f_min = host->ops->get_min_clock(host);
...
}

static const unsigned freqs[] = { 400000, 300000, 200000, 100000 };
void mmc_rescan(struct work_struct *work)
{
...
for (i = 0; i < ARRAY_SIZE(freqs); i++) {
unsigned int freq = freqs[i];
if (freq > host->f_max) {
if (i + 1 < ARRAY_SIZE(freqs))
continue;
freq = host->f_max;
}
if (!mmc_rescan_try_freq(host, max(freq, host->f_min)))
break;
if (freqs[i] <= host->f_min) // If you start at 100K, you will try
400K, 300K, 200K, 100K.
break;
}
...
}

Our controller supports 100K. During the test, it was found that mmc_rescan
failed to scan the card at 400K, and did not try 300K, 200K, and 100K. After
modifying the minimum clock limit to 100K, the card scan was successful.

> >
> > Signed-off-by: Wenchao Chen <wenchao.chen@...soc.com>
> > ---
> >  drivers/mmc/host/sdhci-sprd.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/mmc/host/sdhci-sprd.c b/drivers/mmc/host/sdhci-sprd.c
> > index 46c55ab4884c..b92a408f138d 100644
> > --- a/drivers/mmc/host/sdhci-sprd.c
> > +++ b/drivers/mmc/host/sdhci-sprd.c
> > @@ -309,7 +309,7 @@ static unsigned int sdhci_sprd_get_max_clock(struct sdhci_host *host)
> >
> >  static unsigned int sdhci_sprd_get_min_clock(struct sdhci_host *host)
> >  {
> > -     return 400000;
> > +     return 100000;
> >  }
> >
> >  static void sdhci_sprd_set_uhs_signaling(struct sdhci_host *host,
>