linux-kernel - Re: [PATCH v3 1/2] i2c: davinci: Add PM Runtime Support

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Date:   Tue, 12 Sep 2017 13:55:52 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     Grygorii Strashko <grygorii.strashko@...com>,
        Franklin S Cooper Jr <fcooper@...com>, <wsa@...-dreams.de>,
        <robh+dt@...nel.org>, <linux@...linux.org.uk>,
        <linux-i2c@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <vigneshr@...com>
Subject: Re: [PATCH v3 1/2] i2c: davinci: Add PM Runtime Support

On Tuesday 12 September 2017 01:41 AM, Grygorii Strashko wrote:
> 
> 
> On 09/11/2017 03:07 PM, Franklin S Cooper Jr wrote:
>>
>>
>> On 09/11/2017 06:29 AM, Sekhar Nori wrote:
>>> On Friday 08 September 2017 11:24 PM, Franklin S Cooper Jr wrote:
>>>> 66AK2G has I2C instances that are not apart of the ALWAYS_ON power domain
>>>> like other Keystone 2 SoCs and OMAPL138. Therefore, pm_runtime
>>>
>>> unlike ?
>>>
>>>> is required to insure the power domain used by the specific I2C instance is
>>>> properly turned on along with its functional clock.
>>>>
>>>> Signed-off-by: Franklin S Cooper Jr <fcooper@...com>
>>>> ---
>>>> Version 3 changes:
>>>> Remove several statements that set clk to NULL
>>>> Fix error path
>>>>
>>>>   drivers/i2c/busses/i2c-davinci.c | 64 +++++++++++++++++++++++++++++++++-------
>>>>   1 file changed, 53 insertions(+), 11 deletions(-)
>>>
>>>> @@ -802,12 +821,22 @@ static int davinci_i2c_probe(struct platform_device *pdev)
>>>>   	dev->clk = devm_clk_get(&pdev->dev, NULL);
>>>>   	if (IS_ERR(dev->clk))
>>>>   		return PTR_ERR(dev->clk);
>>>> -	clk_prepare_enable(dev->clk);
>>>>   
>>>>   	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>>>>   	dev->base = devm_ioremap_resource(&pdev->dev, mem);
>>>>   	if (IS_ERR(dev->base)) {
>>>> -		r = PTR_ERR(dev->base);
>>>> +		return PTR_ERR(dev->base);
>>>> +	}
>>>> +
>>>> +	pm_runtime_set_autosuspend_delay(dev->dev,
>>>> +					 DAVINCI_I2C_PM_TIMEOUT);
>>>> +	pm_runtime_use_autosuspend(dev->dev);
>>>> +
>>>> +	pm_runtime_enable(dev->dev);
>>>> +
>>>> +	r = pm_runtime_get_sync(dev->dev);
>>>> +	if (r < 0) {
>>>> +		dev_err(dev->dev, "failed to runtime_get device: %d\n", r);
>>>>   		goto err_unuse_clocks;
>>>
>>> You end up doing a pm_runtime_put_sync() on failure here, instead of
>>> pm_runtime_put_noidle() like rest of the patch.
>>>
>>> May be handle this failure here instead of relying on the goto path.
>>
>> Ok
> 
> I think, it's not necessary - pm_runtime_put_sync() can be used in this case
>  (and used the same way in many other drivers).
> In case, of failure in this place - pm_runtime_put_sync() will just decrement usage counter.

Can you please explain why this is the case? At least on DA850, I see
the runtime_idle callback invoked from rpm_idle() if
pm_runtime_put_sync() is used in the failure path.

Thanks
Sekhar