Re: [PATCH 13/27] ALSA: hda/cs8409: Dont disable I2C clock between consecutive accesses

[Takashi Iwai <tiwai@suse.de>]

On Mon, 26 Jul 2021 19:46:26 +0200,
Vitaly Rodionov wrote:
> 
> From: Lucas Tanure <tanureal@opensource.cirrus.com>
> 
> Only disable I2C clock 25 ms after not being used

This is error-prone and might be racy, I'm afraid.
e.g. the offloaded work isn't canceled when unbinding the driver, so
it'll lead to a use-after-free.  And the work doesn't take a mutex so
it may conflict with re-enabling side.

Above all, there is no description "why" this has to be done so.
Is it about the performance, or any other reason?


thanks,

Takashi

> 
> Signed-off-by: Lucas Tanure <tanureal@opensource.cirrus.com>
> Signed-off-by: Vitaly Rodionov <vitalyr@opensource.cirrus.com>
> ---
>  sound/pci/hda/patch_cs8409.c | 42 +++++++++++++++++++++++-------------
>  sound/pci/hda/patch_cs8409.h |  4 ++++
>  2 files changed, 31 insertions(+), 15 deletions(-)
> 
> diff --git a/sound/pci/hda/patch_cs8409.c b/sound/pci/hda/patch_cs8409.c
> index 08205c19698c..335bcdc69106 100644
> --- a/sound/pci/hda/patch_cs8409.c
> +++ b/sound/pci/hda/patch_cs8409.c
> @@ -53,6 +53,7 @@ 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;
>  	snd_hda_gen_spec_init(&spec->gen);
>  
> @@ -72,21 +73,34 @@ 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);
> +
> +	cs8409_vendor_coef_set(spec->codec, 0x0,
> +			       cs8409_vendor_coef_get(spec->codec, 0x0) & 0xfffffff7);
> +	spec->i2c_clck_enabled = 0;
> +}
> +
> +/*
>   * cs8409_enable_i2c_clock - Enable I2C clocks
>   * @codec: the codec instance
> - * @enable: Enable or disable I2C clocks
> - *
>   * Enable or Disable I2C clocks.
>   */
> -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);
>  
> -	retval = cs8409_vendor_coef_get(codec, 0x0);
> -	newval = (enable) ? (retval | 0x8) : (retval & 0xfffffff7);
> -	cs8409_vendor_coef_set(codec, 0x0, newval);
> +	if (!spec->i2c_clck_enabled) {
> +		cs8409_vendor_coef_set(codec, 0x0, cs8409_vendor_coef_get(codec, 0x0) | 0x8);
> +		spec->i2c_clck_enabled = 1;
> +	}
> +	queue_delayed_work(system_power_efficient_wq, &spec->i2c_clk_work, msecs_to_jiffies(25));
>  }
>  
>  /**
> @@ -134,7 +148,7 @@ static int cs8409_i2c_read(struct hda_codec *codec, unsigned int i2c_address, un
>  	if (spec->cs42l42_suspended)
>  		return -EPERM;
>  
> -	cs8409_enable_i2c_clock(codec, 1);
> +	cs8409_enable_i2c_clock(codec);
>  	cs8409_vendor_coef_set(codec, CS8409_I2C_ADDR, i2c_address);
>  
>  	if (paged) {
> @@ -157,8 +171,6 @@ static int cs8409_i2c_read(struct hda_codec *codec, unsigned int i2c_address, un
>  	/* Register in bits 15-8 and the data in 7-0 */
>  	read_data = cs8409_vendor_coef_get(codec, CS8409_I2C_QREAD);
>  
> -	cs8409_enable_i2c_clock(codec, 0);
> -
>  	return read_data & 0x0ff;
>  }
>  
> @@ -182,7 +194,7 @@ static int cs8409_i2c_write(struct hda_codec *codec, unsigned int i2c_address, u
>  	if (spec->cs42l42_suspended)
>  		return -EPERM;
>  
> -	cs8409_enable_i2c_clock(codec, 1);
> +	cs8409_enable_i2c_clock(codec);
>  	cs8409_vendor_coef_set(codec, CS8409_I2C_ADDR, i2c_address);
>  
>  	if (paged) {
> @@ -203,8 +215,6 @@ static int cs8409_i2c_write(struct hda_codec *codec, unsigned int i2c_address, u
>  		return -EIO;
>  	}
>  
> -	cs8409_enable_i2c_clock(codec, 0);
> -
>  	return 0;
>  }
>  
> @@ -705,6 +715,8 @@ void cs8409_cs42l42_fixups(struct hda_codec *codec, const struct hda_fixup *fix,
>  		spec->cs42l42_mic_jack_in = 0;
>  		spec->cs42l42_suspended = 1;
>  
> +		INIT_DELAYED_WORK(&spec->i2c_clk_work, cs8409_disable_i2c_clock);
> +
>  		/* Basic initial sequence for specific hw configuration */
>  		snd_hda_sequence_write(codec, cs8409_cs42l42_init_verbs);
>  
> diff --git a/sound/pci/hda/patch_cs8409.h b/sound/pci/hda/patch_cs8409.h
> index bf0e8a4cc4cc..542582c213d2 100644
> --- a/sound/pci/hda/patch_cs8409.h
> +++ b/sound/pci/hda/patch_cs8409.h
> @@ -11,6 +11,7 @@
>  
>  #include <linux/pci.h>
>  #include <sound/tlv.h>
> +#include <linux/workqueue.h>
>  #include <sound/hda_codec.h>
>  #include "hda_local.h"
>  #include "hda_auto_parser.h"
> @@ -267,6 +268,7 @@ struct cs8409_cir_param {
>  
>  struct cs8409_spec {
>  	struct hda_gen_spec gen;
> +	struct hda_codec *codec;
>  
>  	unsigned int gpio_mask;
>  	unsigned int gpio_dir;
> @@ -278,6 +280,8 @@ struct cs8409_spec {
>  	s8 vol[CS42L42_VOLUMES];
>  
>  	struct mutex cs8409_i2c_mux;
> +	unsigned int i2c_clck_enabled;
> +	struct delayed_work i2c_clk_work;
>  
>  	/* verb exec op override */
>  	int (*exec_verb)(struct hdac_device *dev, unsigned int cmd, unsigned int flags,
> -- 
> 2.25.1
>