linux-kernel - Re: [PATCH] dmaengine: dw: support for clockless platforms

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Date:	Wed, 11 Feb 2015 14:02:39 +0200
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Russell King <linux@....linux.org.uk>,
	Vinod Koul <vinod.koul@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	dmaengine@...r.kernel.org
Subject: Re: [PATCH] dmaengine: dw: support for clockless platforms

On Wed, 2015-02-11 at 10:10 +0800, Viresh Kumar wrote:
> On Tue, Jan 20, 2015 at 8:57 PM, Heikki Krogerus
> <heikki.krogerus@...ux.intel.com> wrote:
> > When requesting clock in the platform driver, leaving
> > chip->clk value as NULL if -ENOENT is returned, and
> > continue. With other errors returning failure. It makes the
> > driver usable on platforms that do not provide the clock.
> >
> > Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > ---
> >  drivers/dma/dw/platform.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/dma/dw/platform.c b/drivers/dma/dw/platform.c
> > index 32ea1ac..b183bc0 100644
> > --- a/drivers/dma/dw/platform.c
> > +++ b/drivers/dma/dw/platform.c
> > @@ -180,8 +180,12 @@ static int dw_probe(struct platform_device *pdev)
> >         chip->dev = dev;
> >
> >         chip->clk = devm_clk_get(chip->dev, "hclk");
> > -       if (IS_ERR(chip->clk))
> > -               return PTR_ERR(chip->clk);
> > +       if (IS_ERR(chip->clk)) {
> > +               if (PTR_ERR(chip->clk) == -ENOENT)
> > +                       chip->clk = NULL;
> 
> This is wrong and reasons are mentioned in this thread:
> 
> http://lists.infradead.org/pipermail/linux-arm-kernel/2012-March/088437.html

Thanks for the link.

> 
> You don't need to set it to NULL, if CONFIG_HAVE_CLK isn't set
> the dummy routines would take care of it.

Yeah, but in our case we have CONFIG_HAVE_CLK=y and no clk is provided
since IP is clockless. What could you suggest to do in such case?

-- 
Andy Shevchenko <andriy.shevchenko@...el.com>
Intel Finland Oy

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