linux-kernel - Re: [PATCH v2] davinci: vpif: add pm

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Message-ID: <CA+V-a8vFrom92g4CE-Kc2gjK8HSo4xkFwMgfmycSJQib0AF+aQ@mail.gmail.com>
Date:	Mon, 1 Apr 2013 13:53:01 +0530
From:	Prabhakar Lad <prabhakar.csengg@...il.com>
To:	Rajagopal Venkat <rajagopal.venkat@...aro.org>
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>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Sakari Ailus <sakari.ailus@....fi>,
	Sekhar Nori <nsekhar@...com>
Subject: Re: [PATCH v2] davinci: vpif: add pm_runtime support

On Mon, Apr 1, 2013 at 12:47 PM, Rajagopal Venkat
<rajagopal.venkat@...aro.org> wrote:
> On 1 April 2013 12:06, Prabhakar lad <prabhakar.csengg@...il.com> wrote:
>> From: Lad, Prabhakar <prabhakar.csengg@...il.com>
>>
>> Add pm_runtime support to the TI Davinci VPIF driver.
>>
>> Signed-off-by: Lad, Prabhakar <prabhakar.csengg@...il.com>
>> Cc: Mauro Carvalho Chehab <mchehab@...hat.com>
>> Cc: Hans Verkuil <hans.verkuil@...co.com>
>> Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>> Cc: Sakari Ailus <sakari.ailus@....fi>
>> Cc: Sekhar Nori <nsekhar@...com>
>> ---
>>  Changes for v2:
>>  1: Removed use of clk API as pointed by Laurent and Sekhar.
>>
>>  drivers/media/platform/davinci/vpif.c |   24 +++++++-----------------
>>  1 files changed, 7 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/media/platform/davinci/vpif.c b/drivers/media/platform/davinci/vpif.c
>> index 28638a8..599cabb 100644
>> --- a/drivers/media/platform/davinci/vpif.c
>> +++ b/drivers/media/platform/davinci/vpif.c
>> @@ -23,8 +23,8 @@
>>  #include <linux/spinlock.h>
>>  #include <linux/kernel.h>
>>  #include <linux/io.h>
>> -#include <linux/clk.h>
>>  #include <linux/err.h>
>> +#include <linux/pm_runtime.h>
>>  #include <linux/v4l2-dv-timings.h>
>>
>>  #include <mach/hardware.h>
>> @@ -44,7 +44,6 @@ static struct resource        *res;
>>  spinlock_t vpif_lock;
>>
>>  void __iomem *vpif_base;
>> -struct clk *vpif_clk;
>>
>>  /**
>>   * ch_params: video standard configuration parameters for vpif
>> @@ -439,19 +438,15 @@ static int vpif_probe(struct platform_device *pdev)
>>                 goto fail;
>>         }
>>
>> -       vpif_clk = clk_get(&pdev->dev, "vpif");
>> -       if (IS_ERR(vpif_clk)) {
>> -               status = PTR_ERR(vpif_clk);
>> -               goto clk_fail;
>> -       }
>> -       clk_prepare_enable(vpif_clk);
>> +       pm_runtime_enable(&pdev->dev);
>> +       pm_runtime_resume(&pdev->dev);
>> +
>> +       pm_runtime_get(&pdev->dev);
>
> I don't see runtime-pm ops being registered. Can you explain how clock
> prepare/unprepare is taken care by runtime-pm?
>
The pm_runtime API handles the clock management for you.
For Davinci platform runtime PM support for clock management has
been added (You can find it in  arch/arm/mach-davinci/pm_domain.c)
When runtime PM is enabled, the davinci runtime PM implementation will
use the pm_clk layer to enable/disable clocks on demand.

For more/detailed understanding you can go through the pm_runtime framework.

Regards,
--Prabhakar
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