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Date:   Sat, 18 Jun 2022 04:33:19 +0900
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Subject: Re: [PATCH v4 3/4] PM / devfreq: Rework freq_table to be local to
 devfreq struct
Content-Language: en-US
To:     Christian 'Ansuel' Marangi <ansuelsmth@gmail.com>,
        MyungJoo Ham <myungjoo.ham@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        Chanwoo Choi <cw00.choi@samsung.com>,
        Sibi Sankar <sibis@codeaurora.org>,
        Saravana Kannan <skannan@codeaurora.org>,
        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20220614230950.426-1-ansuelsmth@gmail.com>
 <20220614230950.426-4-ansuelsmth@gmail.com>
From:   Chanwoo Choi <cwchoi00@gmail.com>
In-Reply-To: <20220614230950.426-4-ansuelsmth@gmail.com>
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Precedence: bulk

Hi,

Thanks for the good catch. 


I think that this patch fixes issue of commit 0ec09ac2cebe
("PM / devfreq: Set the freq_table of devfreq device").

When some devfreq driver without using passive governor
faces on the all errors including PROBE_DEFER
after executing devfreq_add_device, this issue will happen.

Also need to check the devfreq device driver using freq_table
which was allocated dynamically. In case of devfreq/drivers/exynos-bus.c
used the devfreq->profile->freq_table after devfreq_add_device.

On 22. 6. 15. 08:09, Christian 'Ansuel' Marangi wrote:
> Currently we reference the freq_table to the profile defined one and we
> make changes on it. Devfreq never supported PROBE_DEFER before the cpu
> based scaling support to the passive governor and assumed that a devfreq
> device could only had error and be done with it.
> Now that a device can PROBE_DEFER a rework to the freq_table logic is
> required.
> 
> If a device PROBE_DEFER on the GOV_START, the freq_table is already set
> in the device profile struct and its init is skipped. This is due to the
> fact that it's common for devs to declare this kind of struct static.
> This cause the devfreq logic to find a freq table declared (freq_table
> not NULL) with random data and poiting to the old addrs freed by devm.
 > This problem CAN be solved by devs by clearing the freq_table in their
> profile struct on driver exit path but it should not be trusted and it
> looks to use a flawed logic.
> 
> A better solution is to move the freq_table and max_state to the
> devfreq struct and never change the profile struct.
> This permit to correctly handle PROBE_DEFER since the devfreq struct is
> reallocated and contains new values.
> Also the profile struct should only be used to init the driver and should
> not be used by the devfreq to write the freq_table if it's not provided
> by the driver.
> 

If possible, could you explain the patch description more simply?
Maybe, just focus on the 'freq_table' issue by device managed functions (devs).


> Fixes: a03dacb0316f ("PM / devfreq: Add cpu based scaling support to passive governor")
> Signed-off-by: Christian 'Ansuel' Marangi <ansuelsmth@gmail.com>
> ---
>  drivers/devfreq/devfreq.c          | 71 ++++++++++++++----------------
>  drivers/devfreq/governor_passive.c | 14 +++---
>  include/linux/devfreq.h            |  4 ++
>  3 files changed, 45 insertions(+), 44 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 01474daf4548..2e2b3b414d67 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -123,7 +123,7 @@ void devfreq_get_freq_range(struct devfreq *devfreq,
>  			    unsigned long *min_freq,
>  			    unsigned long *max_freq)
>  {
> -	unsigned long *freq_table = devfreq->profile->freq_table;
> +	unsigned long *freq_table = devfreq->freq_table;
>  	s32 qos_min_freq, qos_max_freq;
>  
>  	lockdep_assert_held(&devfreq->lock);
> @@ -133,11 +133,11 @@ void devfreq_get_freq_range(struct devfreq *devfreq,
>  	 * The devfreq drivers can initialize this in either ascending or
>  	 * descending order and devfreq core supports both.
>  	 */
> -	if (freq_table[0] < freq_table[devfreq->profile->max_state - 1]) {
> +	if (freq_table[0] < freq_table[devfreq->max_state - 1]) {
>  		*min_freq = freq_table[0];
> -		*max_freq = freq_table[devfreq->profile->max_state - 1];
> +		*max_freq = freq_table[devfreq->max_state - 1];
>  	} else {
> -		*min_freq = freq_table[devfreq->profile->max_state - 1];
> +		*min_freq = freq_table[devfreq->max_state - 1];
>  		*max_freq = freq_table[0];
>  	}
>  
> @@ -169,8 +169,8 @@ static int devfreq_get_freq_level(struct devfreq *devfreq, unsigned long freq)
>  {
>  	int lev;
>  
> -	for (lev = 0; lev < devfreq->profile->max_state; lev++)
> -		if (freq == devfreq->profile->freq_table[lev])
> +	for (lev = 0; lev < devfreq->max_state; lev++)
> +		if (freq == devfreq->freq_table[lev])
>  			return lev;
>  
>  	return -EINVAL;
> @@ -178,7 +178,6 @@ static int devfreq_get_freq_level(struct devfreq *devfreq, unsigned long freq)
>  
>  static int set_freq_table(struct devfreq *devfreq)
>  {
> -	struct devfreq_dev_profile *profile = devfreq->profile;
>  	struct dev_pm_opp *opp;
>  	unsigned long freq;
>  	int i, count;
> @@ -188,25 +187,22 @@ static int set_freq_table(struct devfreq *devfreq)
>  	if (count <= 0)
>  		return -EINVAL;
>  
> -	profile->max_state = count;
> -	profile->freq_table = devm_kcalloc(devfreq->dev.parent,
> -					profile->max_state,
> -					sizeof(*profile->freq_table),
> -					GFP_KERNEL);
> -	if (!profile->freq_table) {
> -		profile->max_state = 0;
> +	devfreq->max_state = count;
> +	devfreq->freq_table = devm_kcalloc(devfreq->dev.parent,
> +					   devfreq->max_state,
> +					   sizeof(*devfreq->freq_table),
> +					   GFP_KERNEL);
> +	if (!devfreq->freq_table)
>  		return -ENOMEM;
> -	}
>  
> -	for (i = 0, freq = 0; i < profile->max_state; i++, freq++) {
> +	for (i = 0, freq = 0; i < devfreq->max_state; i++, freq++) {
>  		opp = dev_pm_opp_find_freq_ceil(devfreq->dev.parent, &freq);
>  		if (IS_ERR(opp)) {
> -			devm_kfree(devfreq->dev.parent, profile->freq_table);
> -			profile->max_state = 0;
> +			devm_kfree(devfreq->dev.parent, devfreq->freq_table);
>  			return PTR_ERR(opp);
>  		}
>  		dev_pm_opp_put(opp);
> -		profile->freq_table[i] = freq;
> +		devfreq->freq_table[i] = freq;
>  	}
>  
>  	return 0;
> @@ -246,7 +242,7 @@ int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)
>  
>  	if (lev != prev_lev) {
>  		devfreq->stats.trans_table[
> -			(prev_lev * devfreq->profile->max_state) + lev]++;
> +			(prev_lev * devfreq->max_state) + lev]++;
>  		devfreq->stats.total_trans++;
>  	}
>  
> @@ -835,6 +831,9 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  		if (err < 0)
>  			goto err_dev;
>  		mutex_lock(&devfreq->lock);
> +	} else {
> +		devfreq->freq_table = devfreq->profile->freq_table;
> +		devfreq->max_state = devfreq->profile->max_state;
>  	}
>  
>  	devfreq->scaling_min_freq = find_available_min_freq(devfreq);
> @@ -870,8 +869,8 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  
>  	devfreq->stats.trans_table = devm_kzalloc(&devfreq->dev,
>  			array3_size(sizeof(unsigned int),
> -				    devfreq->profile->max_state,
> -				    devfreq->profile->max_state),
> +				    devfreq->max_state,
> +				    devfreq->max_state),
>  			GFP_KERNEL);
>  	if (!devfreq->stats.trans_table) {
>  		mutex_unlock(&devfreq->lock);
> @@ -880,7 +879,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>  	}
>  
>  	devfreq->stats.time_in_state = devm_kcalloc(&devfreq->dev,
> -			devfreq->profile->max_state,
> +			devfreq->max_state,
>  			sizeof(*devfreq->stats.time_in_state),
>  			GFP_KERNEL);
>  	if (!devfreq->stats.time_in_state) {
> @@ -1665,9 +1664,9 @@ static ssize_t available_frequencies_show(struct device *d,
>  
>  	mutex_lock(&df->lock);
>  
> -	for (i = 0; i < df->profile->max_state; i++)
> +	for (i = 0; i < df->max_state; i++)
>  		count += scnprintf(&buf[count], (PAGE_SIZE - count - 2),
> -				"%lu ", df->profile->freq_table[i]);
> +				"%lu ", df->freq_table[i]);
>  
>  	mutex_unlock(&df->lock);
>  	/* Truncate the trailing space */
> @@ -1690,7 +1689,7 @@ static ssize_t trans_stat_show(struct device *dev,
>  
>  	if (!df->profile)
>  		return -EINVAL;
> -	max_state = df->profile->max_state;
> +	max_state = df->max_state;
>  
>  	if (max_state == 0)
>  		return sprintf(buf, "Not Supported.\n");
> @@ -1707,19 +1706,17 @@ static ssize_t trans_stat_show(struct device *dev,
>  	len += sprintf(buf + len, "           :");
>  	for (i = 0; i < max_state; i++)
>  		len += sprintf(buf + len, "%10lu",
> -				df->profile->freq_table[i]);
> +				df->freq_table[i]);
>  
>  	len += sprintf(buf + len, "   time(ms)\n");
>  
>  	for (i = 0; i < max_state; i++) {
> -		if (df->profile->freq_table[i]
> -					== df->previous_freq) {
> +		if (df->freq_table[i] == df->previous_freq)
>  			len += sprintf(buf + len, "*");
> -		} else {
> +		else
>  			len += sprintf(buf + len, " ");
> -		}
> -		len += sprintf(buf + len, "%10lu:",
> -				df->profile->freq_table[i]);
> +
> +		len += sprintf(buf + len, "%10lu:", df->freq_table[i]);
>  		for (j = 0; j < max_state; j++)
>  			len += sprintf(buf + len, "%10u",
>  				df->stats.trans_table[(i * max_state) + j]);
> @@ -1743,7 +1740,7 @@ static ssize_t trans_stat_store(struct device *dev,
>  	if (!df->profile)
>  		return -EINVAL;
>  
> -	if (df->profile->max_state == 0)
> +	if (df->max_state == 0)
>  		return count;
>  
>  	err = kstrtoint(buf, 10, &value);
> @@ -1751,11 +1748,11 @@ static ssize_t trans_stat_store(struct device *dev,
>  		return -EINVAL;
>  
>  	mutex_lock(&df->lock);
> -	memset(df->stats.time_in_state, 0, (df->profile->max_state *
> +	memset(df->stats.time_in_state, 0, (df->max_state *
>  					sizeof(*df->stats.time_in_state)));
>  	memset(df->stats.trans_table, 0, array3_size(sizeof(unsigned int),
> -					df->profile->max_state,
> -					df->profile->max_state));
> +					df->max_state,
> +					df->max_state));
>  	df->stats.total_trans = 0;
>  	df->stats.last_update = get_jiffies_64();
>  	mutex_unlock(&df->lock);
> diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
> index dcc9dd518197..1810966fd61d 100644
> --- a/drivers/devfreq/governor_passive.c
> +++ b/drivers/devfreq/governor_passive.c
> @@ -145,18 +145,18 @@ static int get_target_freq_with_devfreq(struct devfreq *devfreq,
>  		goto out;
>  
>  	/* Use interpolation if required opps is not available */
> -	for (i = 0; i < parent_devfreq->profile->max_state; i++)
> -		if (parent_devfreq->profile->freq_table[i] == *freq)
> +	for (i = 0; i < parent_devfreq->max_state; i++)
> +		if (parent_devfreq->freq_table[i] == *freq)
>  			break;
>  
> -	if (i == parent_devfreq->profile->max_state)
> +	if (i == parent_devfreq->max_state)
>  		return -EINVAL;
>  
> -	if (i < devfreq->profile->max_state) {
> -		child_freq = devfreq->profile->freq_table[i];
> +	if (i < devfreq->max_state) {
> +		child_freq = devfreq->freq_table[i];
>  	} else {
> -		count = devfreq->profile->max_state;
> -		child_freq = devfreq->profile->freq_table[count - 1];
> +		count = devfreq->max_state;
> +		child_freq = devfreq->freq_table[count - 1];
>  	}
>  
>  out:
> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
> index dc10bee75a72..770a7532655c 100644
> --- a/include/linux/devfreq.h
> +++ b/include/linux/devfreq.h
> @@ -185,6 +185,10 @@ struct devfreq {
>  	struct notifier_block nb;
>  	struct delayed_work work;
>  
> +	/* devfreq local freq_table */
> +	unsigned long *freq_table;
> +	unsigned int max_state;
> +
>  	unsigned long previous_freq;
>  	struct devfreq_dev_status last_status;
>  


-- 
Best Regards,
Samsung Electronics
Chanwoo Choi