linux-kernel - Re: [PATCH] davinci: vpif: add pm

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Date:	Mon, 1 Apr 2013 11:40:06 +0530
From:	Prabhakar Lad <prabhakar.csengg@...il.com>
To:	Sekhar Nori <nsekhar@...com>
Cc:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	DLOS <davinci-linux-open-source@...ux.davincidsp.com>,
	LMML <linux-media@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Sakari Ailus <sakari.ailus@....fi>
Subject: Re: [PATCH] davinci: vpif: add pm_runtime support

Hi Sekhar,

On Mon, Apr 1, 2013 at 11:33 AM, Sekhar Nori <nsekhar@...com> wrote:
> On 3/28/2013 3:50 PM, Prabhakar Lad wrote:
>> Hi Laurent,
>>
>> On Thu, Mar 28, 2013 at 3:40 PM, Laurent Pinchart
>> <laurent.pinchart@...asonboard.com> wrote:
>>> Hi Prabhakar,
>>>
>>> On Thursday 28 March 2013 15:36:11 Prabhakar Lad wrote:
>>>> On Thu, Mar 28, 2013 at 2:39 PM, Laurent Pinchart wrote:
>>>>> On Thursday 28 March 2013 14:20:32 Prabhakar lad wrote:
>>>>>> From: Lad, Prabhakar <prabhakar.csengg@...il.com>
>>>>>>
>>>>>> Add pm_runtime support to the TI Davinci VPIF driver.
>>>>>> Along side this patch replaces clk_get() with devm_clk_get()
>>>>>> to simplify the error handling.
>>>>>>
>>>>>> Signed-off-by: Lad, Prabhakar <prabhakar.csengg@...il.com>
>>>>>> ---
>>>>>>
>>>>>>  drivers/media/platform/davinci/vpif.c |   21 +++++++++++----------
>>>>>>  1 files changed, 11 insertions(+), 10 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/media/platform/davinci/vpif.c
>>>>>> b/drivers/media/platform/davinci/vpif.c index 28638a8..7d14625 100644
>>>>>> --- a/drivers/media/platform/davinci/vpif.c
>>>>>> +++ b/drivers/media/platform/davinci/vpif.c
>>>
>>> [snip]
>>>
>>>>>> @@ -439,12 +440,17 @@ static int vpif_probe(struct platform_device *pdev)
>>>>>>               goto fail;
>>>>>>       }
>>>>>>
>>>>>> -     vpif_clk = clk_get(&pdev->dev, "vpif");
>>>>>> +     vpif_clk = devm_clk_get(&pdev->dev, "vpif");
>>>>>>       if (IS_ERR(vpif_clk)) {
>>>>>>               status = PTR_ERR(vpif_clk);
>>>>>>               goto clk_fail;
>>>>>>       }
>>>>>>
>>>>>> -     clk_prepare_enable(vpif_clk);
>>>>>> +     clk_put(vpif_clk);
>>>>>
>>>>> Why do you need to call clk_put() here ?
>>>>
>>>> The above check is to see if the clock is provided, once done
>>>> we free it using clk_put().
>>>
>>> In that case you shouldn't use devm_clk_get(), otherwise clk_put() will be
>>> called again automatically at remove() time.
>>>
>> Yes agreed it should be clk_get() only.
>>
>>>>>> +     pm_runtime_enable(&pdev->dev);
>>>>>> +     pm_runtime_resume(&pdev->dev);
>>>>>> +
>>>>>> +     pm_runtime_get(&pdev->dev);
>>>>>
>>>>> Does runtime PM automatically handle your clock ? If so can't you remove
>>>>> clock handling from the driver completely ?
>>>>
>>>> Yes  pm runtime take care of enabling/disabling the clocks
>>>> so that we don't have to do it in drivers. I believe clock
>>>> handling is removed with this patch, with just  devm_clk_get() remaining ;)
>>>
>>> When is the clk_get() call expected to fail ? If the clock is provided by the
>>> SoC and always available, can't the check be removed completely ?
>>>
>> Yes I agree with you it can be removed completely assuming the clock
>> is always available from the Soc.
>> But may be I need feedback from others Hans/Sekhar what do you suggest ?
>
> Unless you need the clk handle to get the clock rate or something, you
> should simply rely on runtime PM calls to enable clocks for you and not
> have any clk API call at all in your driver.
>
Thanks this helps!, I'll post a v2 fixing it.

Regards,
--Prabhakar

> Thanks,
> Sekhar
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