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

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Date:	Thu, 28 Mar 2013 11:10:45 +0100
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Prabhakar Lad <prabhakar.csengg@...il.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>
Subject: Re: [PATCH] davinci: vpif: add pm_runtime support

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.

> >> +     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 ?

-- 
Regards,

Laurent Pinchart

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