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

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Message-ID: <6bdaab16-cb16-e039-473c-52dd295bd4ba@ti.com>
Date:   Thu, 4 Jan 2018 20:47:00 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>, <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

Hi,

On Wednesday 03 January 2018 08:47 PM, Marc Kleine-Budde wrote:
> On 01/03/2018 04:06 PM, Faiz Abbas wrote:
>> Hi,
>>
>> On Wednesday 03 January 2018 07:55 PM, Marc Kleine-Budde wrote:
>>> 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.
>>
>> Actually the old clock management (for hclk which is the interface
>> clock) is still required as mentioned in the cover letter. Will change
>> the rather misleading description.
> 
> Ok. So you can use the code as discussed on
> https://patchwork.kernel.org/patch/9436507/ ?

Looking at the kernel configuration, it seems like SAMA5D2 platform
selects CONFIG_PM (Wenyou, please confirm). So, it seems like the only
users of this driver always have CONFIG_PM enabled.

So I guess the best way is to maintain the current code for pm_runtime_*
and move the clock enable/disable to pm_runtime callbacks.

Something like this:

m_can_runtime_resume()
{
	clk_prepare_enable(cclk);
	clk_prepare_enable(hclk);
}

m_can_runtime_suspend()
{
	clk_disable_unprepare(cclk);
	clk_disable_unprepare(hclk);
}

SET_RUNTIME_PM_OPS(m_can_runtime_suspend, m_can_runtime_resume, NULL)

static void m_can_start(struct net_device *dev)
{
	pm_runtime_get_sync(dev)
	...
}

static void m_can_stop(struct net_device *dev)
{
	...
	pm_runtime_put_sync(dev)
}

Does that sound okay? If yes, I will go work on the implementation.

Thanks,
Faiz