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

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Message-ID: <1423657177.31903.505.camel@linux.intel.com>
Date:	Wed, 11 Feb 2015 14:19:37 +0200
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	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 12:07 +0000, Russell King - ARM Linux wrote:
> On Wed, Feb 11, 2015 at 02:02:39PM +0200, Andy Shevchenko wrote:
> > On Wed, 2015-02-11 at 10:10 +0800, Viresh Kumar wrote:
> > > >         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;
> > > 
> > > 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?
> 
> 	chip->clk = devm_clk_get(chip->dev, "hclk");
> 	if (IS_ERR(chip->clk) && PTR_ERR(chip->clk) != -ENOENT)
> 		return PTR_ERR(chip->clk);
> 
> You can then test for the presence of a clk via IS_ERR(chip->clk).
> 
> I'm just debating whether we should add a clk_is_valid() inline function
> to linux/clk.h to avoid these shouting tests, and make it easier for
> people test this in a generic manner.

I guess clock framework may handle whatever is gotten from clk_get(). 
In driver much cleaner to use direct calls with exceptions (like you
can't get a valid clock rate from non-existing clock).
So, what about just passing by the error code and doing nothing?

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

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