Subject: Re: [PATCH v5] can: Convert to runtime_pm

From: Marc Kleine-Budde <[email-masked]>
Date: Tue, 13 Jan 2015 18:44:51 +0100

On 01/13/2015 06:24 PM, Sören Brinkmann wrote:
> On Tue, 2015-01-13 at 06:17PM +0100, Marc Kleine-Budde wrote:
>> On 01/13/2015 06:08 PM, Sören Brinkmann wrote:
>>> On Tue, 2015-01-13 at 12:08PM +0100, Marc Kleine-Budde wrote:
>>>> On 01/12/2015 07:45 PM, Sören Brinkmann wrote:
>>>>> On Mon, 2015-01-12 at 08:34PM +0530, Kedareswara rao Appana wrote:
>>>>>> Instead of enabling/disabling clocks at several locations in the driver,
>>>>>> Use the runtime_pm framework. This consolidates the actions for runtime PM
>>>>>> In the appropriate callbacks and makes the driver more readable and mantainable.
>>>>>>
>>>>>> Signed-off-by: Soren Brinkmann <[email-masked]>
>>>>>> Signed-off-by: Kedareswara rao Appana <[email-masked]>
>>>>>> ---
>>>>>> Changes for v5:
>>>>>>  - Updated with the review comments.
>>>>>>    Updated the remove fuction to use runtime_pm.
>>>>>> Chnages for v4:
>>>>>>  - Updated with the review comments.
>>>>>> Changes for v3:
>>>>>>   - Converted the driver to use runtime_pm.
>>>>>> Changes for v2:
>>>>>>   - Removed the struct platform_device* from suspend/resume
>>>>>>     as suggest by Lothar.
>>>>>>
>>>>>>  drivers/net/can/xilinx_can.c |  157 ++++++++++++++++++++++++++++-------------
>>>>>>  1 files changed, 107 insertions(+), 50 deletions(-)
>>>>> [..]
>>>>>> +static int __maybe_unused xcan_runtime_resume(struct device *dev)
>>>>>>  {
>>>>>> -	struct platform_device *pdev = dev_get_drvdata(dev);
>>>>>> -	struct net_device *ndev = platform_get_drvdata(pdev);
>>>>>> +	struct net_device *ndev = dev_get_drvdata(dev);
>>>>>>  	struct xcan_priv *priv = netdev_priv(ndev);
>>>>>>  	int ret;
>>>>>> +	u32 isr, status;
>>>>>>  
>>>>>>  	ret = clk_enable(priv->bus_clk);
>>>>>>  	if (ret) {
>>>>>> @@ -1014,15 +1030,28 @@ static int __maybe_unused xcan_resume(struct device *dev)
>>>>>>  	ret = clk_enable(priv->can_clk);
>>>>>>  	if (ret) {
>>>>>>  		dev_err(dev, "Cannot enable clock.\n");
>>>>>> -		clk_disable_unprepare(priv->bus_clk);
>>>>>> +		clk_disable(priv->bus_clk);
>>>>> [...]
>>>>>> @@ -1173,12 +1219,23 @@ static int xcan_remove(struct platform_device *pdev)
>>>>>>  {
>>>>>>  	struct net_device *ndev = platform_get_drvdata(pdev);
>>>>>>  	struct xcan_priv *priv = netdev_priv(ndev);
>>>>>> +	int ret;
>>>>>> +
>>>>>> +	ret = pm_runtime_get_sync(&pdev->dev);
>>>>>> +	if (ret < 0) {
>>>>>> +		netdev_err(ndev, "%s: pm_runtime_get failed(%d)\n",
>>>>>> +				__func__, ret);
>>>>>> +		return ret;
>>>>>> +	}
>>>>>>  
>>>>>>  	if (set_reset_mode(ndev) < 0)
>>>>>>  		netdev_err(ndev, "mode resetting failed!\n");
>>>>>>  
>>>>>>  	unregister_candev(ndev);
>>>>>> +	pm_runtime_disable(&pdev->dev);
>>>>>>  	netif_napi_del(&priv->napi);
>>>>>> +	clk_disable_unprepare(priv->bus_clk);
>>>>>> +	clk_disable_unprepare(priv->can_clk);
>>>>>
>>>>> Shouldn't pretty much all these occurrences of clk_disable/enable
>>>>> disappear? This should all be handled by the runtime_pm framework now.
>>>>
>>>> We have:
>>>> - clk_prepare_enable() in probe
>>>
>>> This should become something like pm_runtime_get_sync(), shouldn't it?
>>>
>>>> - clk_disable_unprepare() in remove
>>>
>>> pm_runtime_put()
>>>
>>>> - clk_enable() in runtime_resume
>>>> - clk_disable() in runtime_suspend
>>>
>>> These are the ones needed.
>>>
>>> The above makes me suspect that the clocks are always on, regardless of
>>
>> Define "on" :)
>> The clocks are prepared after probe() exists, but not enabled. The first
>> pm_runtime_get_sync() will enable the clocks.
>>
>>> the runtime suspend state since they are enabled in probe and disabled
>>> in remove, is that right? Ideally, the usage in probe and remove should
>>> be migrated to runtime_pm and clocks should really only be running when
>>> needed and not throughout the whole lifetime of the driver.
>>
>> The clocks are not en/disabled via pm_runtime, because
>> pm_runtime_get_sync() is called from atomic contect. We can have another
>> look into the driver and try to change this.

> Wasn't that why the call to pm_runtime_irq_safe() was added?

Good question. That should be investigated.

> Also, clk_enable/disable should be okay to be run from atomic context.
> And if the clock are already prepared after the exit of probe that
> should be enough. Then remove() should just have to do the unprepare.
> But I don't see why runtime_pm shouldn't be able to do the
> enable/disable.

runtime_pm does call the clk_{enable,disable} function. But you mean
clk_prepare() + pm_runtime_get_sync() should be used in probe() instead
of calling clk_prepare_enable(). Good idea! I think the
"pm_runtime_set_active(&pdev->dev);" has to be removed from the patch.

Coming back whether blocking calls are allowed or not.
If you make a call to pm_runtime_irq_safe(), you state that it's okay to
call pm_runtime_get_sync() from atomic context. But it's only called in
open, probe, remove and in xcan_get_berr_counter, which is not called
from atomic either. So let's try to remove the pm_runtime_irq_safe() and
use clk_prepare_enable() clk_disable_unprepare() in the runtime_resume()
runtime_suspend() functions.

Marc

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