Re: [PATCH V2] PM / OPP: predictable fail results for opp_find* functions

[Rafael J. Wysocki]

On Monday 22 of October 2012 08:33:19 Nishanth Menon wrote:
> Currently the opp_find* functions return -ENODEV when:
> a) it cant find a device (e.g. request for an OPP search on device
>    which was not registered)
> b) When it cant find a match for the search strategy used
> 
> This makes life a little in-efficient for users such as devfreq
> to make reasonable judgement before switching search strategies.
> 
> So, standardize the return results as following:
>  -EINVAL for bad pointer parameters
>  -ENODEV when device cannot be found
>  -ERANGE when search fails
> 
> This has the following benefit for devfreq implementation:
> The search fails when an unregistered device pointer is provided.
> This is a trigger to change the search direction and search for
> a better fit, however, if we cannot differentiate between a valid
> search range failure Vs an unregistered device, second search goes
> through the same fail return condition. This can be avoided by
> appropriate handling of error return code.
> 
> With this change, we also fix devfreq for the improved search
> strategy with updated error code.
> 
> Cc: MyungJoo Ham <myungjoo.ham@xxxxxxxxxxx>
> Cc: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
> Cc: "Rafael J. Wysocki" <rjw@xxxxxxx>
> Cc: Kevin Hilman <khilman@xxxxxx>
> Cc: linux-pm@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> 
> Reviewed-by: Kevin Hilman <khilman@xxxxxx>
> Acked-by: MyungJoo Ham <myungjoo.ham@xxxxxxxxxxx>
> Signed-off-by: Nishanth Menon <nm@xxxxxx>

Applied to linux-pm.git/linux-next as v3.8 material.

Thanks,
Rafael


> ---
> V2:
>  * commit message change - updated frome example code, to verbose description
>  * picked up Acked-by and Reviewed-by tags from V1.
>  * rebased to v3.7-rc2
> V1: https://patchwork.kernel.org/patch/1582111/
> 
>  drivers/base/power/opp.c  |   27 +++++++++++++++++++--------
>  drivers/devfreq/devfreq.c |    4 ++--
>  2 files changed, 21 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/base/power/opp.c b/drivers/base/power/opp.c
> index 4730a58..99d0573 100644
> --- a/drivers/base/power/opp.c
> +++ b/drivers/base/power/opp.c
> @@ -234,7 +234,10 @@ EXPORT_SYMBOL(opp_get_opp_count);
>   *
>   * Searches for exact match in the opp list and returns pointer to the matching
>   * opp if found, else returns ERR_PTR in case of error and should be handled
> - * using IS_ERR.
> + * using IS_ERR. Error return values can be:
> + * EINVAL:	for bad pointer
> + * ERANGE:	no match found for search
> + * ENODEV:	if device not found in list of registered devices
>   *
>   * Note: available is a modifier for the search. if available=true, then the
>   * match is for exact matching frequency and is available in the stored OPP
> @@ -253,7 +256,7 @@ struct opp *opp_find_freq_exact(struct device *dev, unsigned long freq,
>  				bool available)
>  {
>  	struct device_opp *dev_opp;
> -	struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);
> +	struct opp *temp_opp, *opp = ERR_PTR(-ERANGE);
>  
>  	dev_opp = find_device_opp(dev);
>  	if (IS_ERR(dev_opp)) {
> @@ -283,7 +286,11 @@ EXPORT_SYMBOL(opp_find_freq_exact);
>   * for a device.
>   *
>   * Returns matching *opp and refreshes *freq accordingly, else returns
> - * ERR_PTR in case of error and should be handled using IS_ERR.
> + * ERR_PTR in case of error and should be handled using IS_ERR. Error return
> + * values can be:
> + * EINVAL:	for bad pointer
> + * ERANGE:	no match found for search
> + * ENODEV:	if device not found in list of registered devices
>   *
>   * Locking: This function must be called under rcu_read_lock(). opp is a rcu
>   * protected pointer. The reason for the same is that the opp pointer which is
> @@ -294,7 +301,7 @@ EXPORT_SYMBOL(opp_find_freq_exact);
>  struct opp *opp_find_freq_ceil(struct device *dev, unsigned long *freq)
>  {
>  	struct device_opp *dev_opp;
> -	struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);
> +	struct opp *temp_opp, *opp = ERR_PTR(-ERANGE);
>  
>  	if (!dev || !freq) {
>  		dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
> @@ -303,7 +310,7 @@ struct opp *opp_find_freq_ceil(struct device *dev, unsigned long *freq)
>  
>  	dev_opp = find_device_opp(dev);
>  	if (IS_ERR(dev_opp))
> -		return opp;
> +		return ERR_CAST(dev_opp);
>  
>  	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
>  		if (temp_opp->available && temp_opp->rate >= *freq) {
> @@ -326,7 +333,11 @@ EXPORT_SYMBOL(opp_find_freq_ceil);
>   * for a device.
>   *
>   * Returns matching *opp and refreshes *freq accordingly, else returns
> - * ERR_PTR in case of error and should be handled using IS_ERR.
> + * ERR_PTR in case of error and should be handled using IS_ERR. Error return
> + * values can be:
> + * EINVAL:	for bad pointer
> + * ERANGE:	no match found for search
> + * ENODEV:	if device not found in list of registered devices
>   *
>   * Locking: This function must be called under rcu_read_lock(). opp is a rcu
>   * protected pointer. The reason for the same is that the opp pointer which is
> @@ -337,7 +348,7 @@ EXPORT_SYMBOL(opp_find_freq_ceil);
>  struct opp *opp_find_freq_floor(struct device *dev, unsigned long *freq)
>  {
>  	struct device_opp *dev_opp;
> -	struct opp *temp_opp, *opp = ERR_PTR(-ENODEV);
> +	struct opp *temp_opp, *opp = ERR_PTR(-ERANGE);
>  
>  	if (!dev || !freq) {
>  		dev_err(dev, "%s: Invalid argument freq=%p\n", __func__, freq);
> @@ -346,7 +357,7 @@ struct opp *opp_find_freq_floor(struct device *dev, unsigned long *freq)
>  
>  	dev_opp = find_device_opp(dev);
>  	if (IS_ERR(dev_opp))
> -		return opp;
> +		return ERR_CAST(dev_opp);
>  
>  	list_for_each_entry_rcu(temp_opp, &dev_opp->opp_list, node) {
>  		if (temp_opp->available) {
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 0920d75..bee1c29 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -656,14 +656,14 @@ struct opp *devfreq_recommended_opp(struct device *dev, unsigned long *freq,
>  		opp = opp_find_freq_floor(dev, freq);
>  
>  		/* If not available, use the closest opp */
> -		if (opp == ERR_PTR(-ENODEV))
> +		if (opp == ERR_PTR(-ERANGE))
>  			opp = opp_find_freq_ceil(dev, freq);
>  	} else {
>  		/* The freq is an lower bound. opp should be higher */
>  		opp = opp_find_freq_ceil(dev, freq);
>  
>  		/* If not available, use the closest opp */
> -		if (opp == ERR_PTR(-ENODEV))
> +		if (opp == ERR_PTR(-ERANGE))
>  			opp = opp_find_freq_floor(dev, freq);
>  	}
>  
> 
-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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