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

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Message-ID: <CA+V-a8sWCx1CpDbtDHVZKGpW2z1FrPpY1o3UJaoU6nEK9RN=Ug@mail.gmail.com>
Date:	Thu, 28 Mar 2013 15:50:55 +0530
From:	Prabhakar Lad <prabhakar.csengg@...il.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	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>,
	Sekhar Nori <nsekhar@...com>
Subject: Re: [PATCH] davinci: vpif: add pm_runtime support

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 ?

Regards,
--Prabhakar

> --
> Regards,
>
> Laurent Pinchart
>
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