linux-kernel - Re: [PATCH v2 5/7] dmaengine: dw: platform: power on device on shutdown

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Date:	Thu, 26 Nov 2015 23:11:57 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-acpi@...r.kernel.org, dmaengine@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH v2 5/7] dmaengine: dw: platform: power on device on
 shutdown

On Thu, Nov 26, 2015 at 07:24:48PM +0200, Andy Shevchenko wrote:
> On Thu, 2015-11-26 at 22:31 +0530, Vinod Koul wrote:
> > On Thu, Nov 26, 2015 at 05:19:11PM +0200, Andy Shevchenko wrote:
> > > We have to call dw_dma_disable() to stop any ongoing transfer.
> > 
> > Ok
> > 
> > > On some platforms we can't do that since DMA device is powered off.
> > 
> > Umm, you said we have ongoing transfer which means DMA should be
> > on..!!
> 
> Yes, that's true for HSW/BDW and non-affected BYT/CHT.

Can you please explain even when DMA is in use how can device be powered
off? That does not sound right to me. Is this on GP DMA on BYT/CHT or
something else?

> 
> Like I mentioned here is no possibility to know which platform we run
> on.
> 
> Would you like to test this on a real device? We can provide you a
> login.
> 
> > 
> > > Moreover we have no
> > > possibility at that point to check if the platform is affected or
> > > not. That's
> > > why we call pm_runtime_get_sync() / pm_runtime_put()
> > > unconditionally. On the
> > > other hand we can't use pm_runtime_suspended() because runtime PM
> > > framework is
> > > not fully used by the driver.
> > 
> > Shouldn't that be fixed?
> 
> Do you have any solution how?
> 
> Rough approach is to turn on it on channel allocation and turn off on
> freeing resources. The obvious downside of this solution is power
> consumption of idling device.

But in that case, the clients should not hold ref of dma chan when idle and
allocate only when required which is a resonable expectation

> 
> In any case it might be done in the future and it's not a scope of this
> series.

Sounds fine to me
> 
> > 
> > > 
> > > Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > > ---
> > >  drivers/dma/dw/platform.c | 12 ++++++++++++
> > >  1 file changed, 12 insertions(+)
> > > 
> > > diff --git a/drivers/dma/dw/platform.c b/drivers/dma/dw/platform.c
> > > index 68a4815..d0734e9 100644
> > > --- a/drivers/dma/dw/platform.c
> > > +++ b/drivers/dma/dw/platform.c
> > > @@ -239,7 +239,19 @@ static void dw_shutdown(struct platform_device
> > > *pdev)
> > >  {
> > >  	struct dw_dma_chip *chip = platform_get_drvdata(pdev);
> > >  
> > > +	/*
> > > +	 * We have to call dw_dma_disable() to stop any ongoing
> > > transfer. On
> > > +	 * some platforms we can't do that since DMA device is
> > > powered off.
> > > +	 * Moreover we have no possibility to check if the
> > > platform is affected
> > > +	 * or not. That's why we call pm_runtime_get_sync() /
> > > pm_runtime_put()
> > > +	 * unconditionally. On the other hand we can't use
> > > +	 * pm_runtime_suspended() because runtime PM framework is
> > > not fully
> > > +	 * used by the driver.
> > > +	 */
> > > +	pm_runtime_get_sync(chip->dev);
> > >  	dw_dma_disable(chip);
> > > +	pm_runtime_put_sync_suspend(chip->dev);
> > > +
> > >  	clk_disable_unprepare(chip->clk);
> > >  }
> > >  
> > > -- 
> > > 2.6.2
> > > 
> > 
> 
> -- 
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Intel Finland Oy
> 

-- 
~Vinod
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