linux-kernel - Re: [PATCH v6 3/6] can: m

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Message-ID: <7d857263-14a7-6001-8f13-42d80f757573@pengutronix.de>
Date:   Wed, 3 Jan 2018 15:25:22 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Faiz Abbas <faiz_abbas@...com>, wg@...ndegger.com,
        robh+dt@...nel.org, mark.rutland@....com
Cc:     linux-can@...r.kernel.org, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        nsekhar@...com, fcooper@...com, robh@...nel.org,
        Wenyou.Yang@...rochip.com, sergei.shtylyov@...entembedded.com
Subject: Re: [PATCH v6 3/6] can: m_can: Add PM Runtime

On 01/03/2018 01:39 PM, Faiz Abbas wrote:
> On Tuesday 02 January 2018 09:37 PM, Marc Kleine-Budde wrote:
>> On 12/22/2017 02:31 PM, Faiz Abbas wrote:
>>> From: Franklin S Cooper Jr <fcooper@...com>
>>>
>>> Add support for PM Runtime which is the new way to handle managing clocks.
>>> However, to avoid breaking SoCs not using PM_RUNTIME leave the old clk
>>> management approach in place.
>>
>> There is no PM_RUNTIME anymore since 464ed18ebdb6 ("PM: Eliminate
>> CONFIG_PM_RUNTIME")
> 
> Ok. Will change the commit message.
> 
>>
>> Have a look at the discussion: https://patchwork.kernel.org/patch/9436507/ :
>>
>>>> Well, I admit it would be nicer if drivers didn't have to worry about 
>>>> whether or not CONFIG_PM was enabled.  A slightly cleaner approach 
>>>> from the one outlined above would have the probe routine do this:
>>>>
>>>> 	my_power_up(dev);
>>>> 	pm_runtime_set_active(dev);
>>>> 	pm_runtime_get_noresume(dev);
>>>> 	pm_runtime_enable(dev);
> 
> This discussion seems to be about cases in which CONFIG_PM is not
> enabled. CONFIG_PM is always selected in the case of omap devices.

Yes, but in the commit message you state that you need to support
systems that don't have PM_RUNTIME enabled. The only mainline SoCs I see
is "arch/arm/boot/dts/sama5d2.dtsi" so far. Please check if they select
CONFIG_PM, then we can make the driver much simpler.

>>> PM_RUNTIME is required by OMAP based devices to handle clock management.
>>> Therefore, this allows future Texas Instruments SoCs that have the MCAN IP
>>> to work with this driver.
>>
>> Who will set the SET_RUNTIME_PM_OPS in this case?
> 
> It is set with a common SET_RUNTIME_PM_OPS in the case of omap at
> arch/arm/mach-omap2/omap_device.c:632
> 
> struct dev_pm_domain omap_device_pm_domain = {
>         .ops = {
>                 SET_RUNTIME_PM_OPS(_od_runtime_suspend, _od_runtime_resume,
>                                    NULL)
>                 USE_PLATFORM_PM_SLEEP_OPS
>                 SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(_od_suspend_noirq,
>                                               _od_resume_noirq)
>         }
> };
> 
> 
>>
>>> Signed-off-by: Franklin S Cooper Jr <fcooper@...com>
>>> [nsekhar@...com: handle pm_runtime_get_sync() failure, fix some bugs]
>>> Signed-off-by: Sekhar Nori <nsekhar@...com>
>>> Signed-off-by: Faiz Abbas <faiz_abbas@...com>
>>> ---
>>>  drivers/net/can/m_can/m_can.c | 38 ++++++++++++++++++++++++++++++++++----
>>>  1 file changed, 34 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
>>> index f72116e..53e764f 100644
>>> --- a/drivers/net/can/m_can/m_can.c
>>> +++ b/drivers/net/can/m_can/m_can.c
>>> @@ -23,6 +23,7 @@
>>>  #include <linux/of.h>
>>>  #include <linux/of_device.h>
>>>  #include <linux/platform_device.h>
>>> +#include <linux/pm_runtime.h>
>>>  #include <linux/iopoll.h>
>>>  #include <linux/can/dev.h>
>>>  
>>> @@ -625,19 +626,33 @@ static int m_can_clk_start(struct m_can_priv *priv)
>>>  {
>>>  	int err;
>>>  
>>> +	err = pm_runtime_get_sync(priv->device);
>>> +	if (err) {
>>> +		pm_runtime_put_noidle(priv->device);
>>
>> Why do you call this in case of an error?
> 
> pm_runtime_get_sync() increments the usage count of the device before
> any error is returned. This needs to be decremented using
> pm_runtime_put_noidle().

Oh, I'm curious how many drivers don't get this right.

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
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