linux-kernel - Re: [PATCH] ASoC: rt5682: Prefer async probe

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Message-ID: <CAFv8NwL-s0c_nFWKHmBKgPVeLXwGWdgV+fUtw8MLBJw2D3ox1w@mail.gmail.com>
Date:   Sun, 30 Aug 2020 19:04:42 +0800
From:   Cheng-yi Chiang <cychiang@...omium.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Mark Brown <broonie@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
        Liam Girdwood <lgirdwood@...il.com>,
        Oder Chiou <oder_chiou@...ltek.com>,
        Takashi Iwai <tiwai@...e.com>,
        "moderated list:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM..." 
        <alsa-devel@...a-project.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: rt5682: Prefer async probe

On Sat, Aug 29, 2020 at 7:20 AM Douglas Anderson <dianders@...omium.org> wrote:
>
> The probe of rt5682 is pretty slow.  A quick measurement shows that it
> takes ~650 ms on at least one board.  There's no reason to block all
> other drivers waiting for this probe to finish.  Set the flag to allow
> other drivers to probe while we're probing.
>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> NOTE: I haven't done any analysis of the driver to see _why_ it's so
> slow, only that I have measured it to be slow.  Someone could
> certainly take the time to profile / optimize it, but in any case it
> still won't hurt to be async.


Hi Doug, thank you for the fix.

There are multiple usleep in the probe of rt5682 driver.
The major one is a 300 ms sleep after the regulator turns on.
There are other sleeps for several tens of ms.
>
>
> This is a very safe flag to turn on since:
>
> 1. It's not like our probe order was defined by anything anyway.  When
> we probe is at the whim of when our i2c controller probes and that can
> be any time.
>
> 2. If some other driver needs us then they have to handle the fact
> that we might not have probed yet anyway.


Agree.
soc-core already handled this by returning -EPROBE_DEFER when a
component is not found.
So the machine driver can probe again.
Even in the current behavior, we already see machine driver probe
again when the codec driver is not ready,
so I think adding this async flag will not affect the machine driver.

>
>
> 3. There may be other drivers probing at the same time as us anyway
> because _they_ used async probe.
>
> While I won't say that it's impossible to tickle a bug by turning on
> async probe, I would assert that in almost all cases the bug was
> already there and needed to be fixed anyway.
>
>  sound/soc/codecs/rt5682-i2c.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/sound/soc/codecs/rt5682-i2c.c b/sound/soc/codecs/rt5682-i2c.c
> index 85aba311bdc8..6b4e0eb30c89 100644
> --- a/sound/soc/codecs/rt5682-i2c.c
> +++ b/sound/soc/codecs/rt5682-i2c.c
> @@ -294,6 +294,7 @@ static struct i2c_driver rt5682_i2c_driver = {
>                 .name = "rt5682",
>                 .of_match_table = rt5682_of_match,
>                 .acpi_match_table = rt5682_acpi_match,
> +               .probe_type = PROBE_PREFER_ASYNCHRONOUS,


One thing I am wondering is that there has not been any usage in codec
driver for this.
I think every codec driver can use this, and take the benefit of a
possible faster boot time ?

>
>         },
>         .probe = rt5682_i2c_probe,
>         .shutdown = rt5682_i2c_shutdown,
> --
> 2.28.0.402.g5ffc5be6b7-goog
>