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From: Takashi Iwai <tiwai@suse.de>
To: Vitaly Rodionov <vitalyr@opensource.cirrus.com>
Cc: Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
	<alsa-devel@alsa-project.org>, <patches@opensource.cirrus.com>,
	<linux-kernel@vger.kernel.org>,
	Lucas Tanure <tanureal@opensource.cirrus.com>,
	Stefan Binding <sbinding@opensource.cirrus.com>
Subject: Re: [PATCH v2 13/27] ALSA: hda/cs8409: Dont disable I2C clock between consecutive accesses
Date: Thu, 29 Jul 2021 11:48:24 +0200	[thread overview]
Message-ID: <s5him0ta1sn.wl-tiwai@suse.de> (raw)
In-Reply-To: <20210728134408.369396-14-vitalyr@opensource.cirrus.com>

On Wed, 28 Jul 2021 15:43:54 +0200,
Vitaly Rodionov wrote:
> 
> From: Lucas Tanure <tanureal@opensource.cirrus.com>
> 
> Only disable I2C clock 25 ms after not being used.
> 
> The current implementation enables and disables the I2C clock for each
> I2C transaction. Each enable/disable call requires two verb transactions.
> This means each I2C transaction requires a total of four verb transactions
> to enable and disable the clock.
> However, if there are multiple consecutive I2C transactions, it is not
> necessary to enable and disable the clock each time, instead it is more
> efficient to enable the clock for the first transaction, and disable it
> after the final transaction, which would improve performance.
> This is achieved by using a timeout which disables the clock if no request
> to enable the clock has occurred for 25 ms.
> 
> Signed-off-by: Lucas Tanure <tanureal@opensource.cirrus.com>
> Signed-off-by: Vitaly Rodionov <vitalyr@opensource.cirrus.com>
> Signed-off-by: Stefan Binding <sbinding@opensource.cirrus.com>
> 
> Changes in v2:
> Improved delayed work start/cancel implementation, and re-worked commit message
> adding more explanation why this was required. 
> 
> 
> ---
>  sound/pci/hda/patch_cs8409.c | 56 +++++++++++++++++++++++++-----------
>  sound/pci/hda/patch_cs8409.h |  4 +++
>  2 files changed, 43 insertions(+), 17 deletions(-)
> 
> diff --git a/sound/pci/hda/patch_cs8409.c b/sound/pci/hda/patch_cs8409.c
> index 08205c19698c..fafc0f309e70 100644
> --- a/sound/pci/hda/patch_cs8409.c
> +++ b/sound/pci/hda/patch_cs8409.c
> @@ -53,7 +53,9 @@ static struct cs8409_spec *cs8409_alloc_spec(struct hda_codec *codec)
>  	if (!spec)
>  		return NULL;
>  	codec->spec = spec;
> +	spec->codec = codec;
>  	codec->power_save_node = 1;
> +	INIT_DELAYED_WORK(&spec->i2c_clk_work, cs8409_disable_i2c_clock);
>  	snd_hda_gen_spec_init(&spec->gen);
>  
>  	return spec;
> @@ -72,21 +74,37 @@ static inline void cs8409_vendor_coef_set(struct hda_codec *codec, unsigned int
>  	snd_hda_codec_write(codec, CS8409_PIN_VENDOR_WIDGET, 0, AC_VERB_SET_PROC_COEF, coef);
>  }
>  
> -/**
> +/*
> + * cs8409_disable_i2c_clock - Worker that disable the I2C Clock after 25ms without use
> + */
> +static void cs8409_disable_i2c_clock(struct work_struct *work)
> +{
> +	struct cs8409_spec *spec = container_of(work, struct cs8409_spec, i2c_clk_work.work);
> +
> +	mutex_lock(&spec->cs8409_i2c_mux);
> +	cs8409_vendor_coef_set(spec->codec, 0x0,
> +			       cs8409_vendor_coef_get(spec->codec, 0x0) & 0xfffffff7);
> +	spec->i2c_clck_enabled = 0;
> +	mutex_unlock(&spec->cs8409_i2c_mux);

Here we have a lock in the work, and this would become a problem in
the below...

> +}
> +
> +/*
>   * cs8409_enable_i2c_clock - Enable I2C clocks
>   * @codec: the codec instance
> - * @enable: Enable or disable I2C clocks
> - *
>   * Enable or Disable I2C clocks.
> + * This must be called when the i2c mutex is locked.
>   */
> -static void cs8409_enable_i2c_clock(struct hda_codec *codec, unsigned int enable)
> +static void cs8409_enable_i2c_clock(struct hda_codec *codec)
>  {
> -	unsigned int retval;
> -	unsigned int newval;
> +	struct cs8409_spec *spec = codec->spec;
> +
> +	cancel_delayed_work_sync(&spec->i2c_clk_work);

Here, cancel_delayed_work_sync().  Since it's called inside the mutex
mutex (taken in the caller side), it'll lead to a deadlock.

(I know the i2c mutex lock is moved to this function in a later patch,
but this makes harder to review.  Given that it's only about the
performance, it'd better to apply this kind of change at the end of
series, not in the middle.)

In general, making such an async handling really race-free is not that
trivial.  Even if you call cancel_delayed_work_sync() outside the
mutex, it's possible that another task wedges itself between
cancel_work() and the mutex lock and re-enables the work.

One easier alternative implementation would be rather to allow enable
/ disable clock reentrant with refcounting.  It accepts the function
sequence like:

	enable_clock();
	i2c_write();
	i2c_write();
	...
	disable_clock();

while another thread calls

	enable_clock();
	i2c_write();
	disable_clock();

at the same time.


thanks,

Takashi

  reply	other threads:[~2021-07-29  9:48 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-28 13:43 [PATCH v2 00/27] ALSA: hda/cirrus: Split generic cirrus HDA codecs and CS8490 bridge into separate modules Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 01/27] ALSA: hda/cirrus: Move CS8409 HDA bridge to separate module Vitaly Rodionov
2021-07-29  9:50   ` Takashi Iwai
2021-07-28 13:43 ` [PATCH v2 02/27] ALSA: hda/cs8409: Move arrays of configuration to a new file Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 03/27] ALSA: hda/cs8409: Use enums for register names and coefficients Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 04/27] ALSA: hda/cs8409: Mask all CS42L42 interrupts on initialization Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 05/27] ALSA: hda/cs8409: Reduce HS pops/clicks for Cyborg Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 06/27] ALSA: hda/cs8409: Disable unnecessary Ring Sense for Cyborg/Warlock/Bullseye Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 07/27] ALSA: hda/cs8409: Disable unsolicited responses during suspend Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 08/27] ALSA: hda/cs8409: Disable unsolicited response for the first boot Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 09/27] ALSA: hda/cs8409: Mask CS42L42 wake events Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 10/27] ALSA: hda/cs8409: Simplify CS42L42 jack detect Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 11/27] ALSA: hda/cs8409: Prevent I2C access during suspend time Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 12/27] ALSA: hda/cs8409: Generalize volume controls Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 13/27] ALSA: hda/cs8409: Dont disable I2C clock between consecutive accesses Vitaly Rodionov
2021-07-29  9:48   ` Takashi Iwai [this message]
2021-07-28 13:43 ` [PATCH v2 14/27] ALSA: hda/cs8409: Avoid setting the same I2C address for every access Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 15/27] ALSA: hda/cs8409: Avoid re-setting the same page as the last access Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 16/27] ALSA: hda/cs8409: Support i2c bulk read/write functions Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 17/27] ALSA: hda/cs8409: Separate CS8409, CS42L42 and project functions Vitaly Rodionov
2021-07-28 13:43 ` [PATCH v2 18/27] ALSA: hda/cs8409: Move codec properties to its own struct Vitaly Rodionov
2021-07-28 13:44 ` [PATCH v2 19/27] ALSA: hda/cs8409: Support multiple sub_codecs for Suspend/Resume/Unsol events Vitaly Rodionov
2021-07-28 13:44 ` [PATCH v2 20/27] ALSA: hda/cs8409: Add Support to disable jack type detection for CS42L42 Vitaly Rodionov
2021-07-28 13:44 ` [PATCH v2 21/27] ALSA: hda/cs8409: Add support for dolphin Vitaly Rodionov
2021-07-28 13:44 ` [PATCH v2 22/27] ALSA: hda/cs8409: Enable Full Scale Volume for Line Out Codec on Dolphin Vitaly Rodionov
2021-07-28 13:44 ` [PATCH v2 23/27] ALSA: hda/cs8409: Set fixed sample rate of 48kHz for CS42L42 Vitaly Rodionov
2021-07-28 13:44 ` [PATCH v2 24/27] ALSA: hda/cs8409: Use timeout rather than retries for I2C transaction waits Vitaly Rodionov
2021-07-28 13:44 ` [PATCH v2 25/27] ALSA: hda/cs8409: Remove unnecessary delays Vitaly Rodionov
2021-07-28 13:44 ` [PATCH v2 26/27] ALSA: hda/cs8409: Follow correct CS42L42 power down sequence for suspend Vitaly Rodionov
2021-07-28 13:44 ` [PATCH v2 27/27] ALSA: hda/cs8409: Unmute/Mute codec when stream starts/stops Vitaly Rodionov

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