[PATCH 01/11] usb: chipidea: Add power management support

[Sascha Hauer]

On Mon, Oct 14, 2013 at 05:04:21PM +0800, Peter Chen wrote:
> On Mon, Oct 14, 2013 at 10:42:16AM +0200, Sascha Hauer wrote:
> > On Mon, Oct 14, 2013 at 03:55:48PM +0800, Peter Chen wrote:
> > > On Mon, Oct 14, 2013 at 10:04:58AM +0200, Lothar Waßmann wrote:
> > > > Hi,
> > > > 
> > > > Peter Chen wrote:
> > > > > This commit adds runtime and system power management support for
> > > > > chipidea core. The runtime pm support is controlled by glue
> > > > > layer, it can be enabled by flag CI_HDRC_SUPPORTS_RUNTIME_PM.
> > > > > 
> > > > [...]
> > > > > +#ifdef CONFIG_PM
> > > > > +static int ci_controller_suspend(struct device *dev)
> > > > > +{
> > > > > +	struct ci_hdrc *ci = dev_get_drvdata(dev);
> > > > > +
> > > > > +	dev_dbg(dev, "at %s\n", __func__);
> > > > > +
> > > > > +	if (atomic_read(&ci->in_lpm))
> > > > > +		return 0;
> > > > > +
> > > > What does this 'atomic_read()' buy you over just testing/assinging a
> > > > simple integer. Note that just because the function has 'atomic' in
> > > > its name the sequence:
> > > > 	atomic_read();
> > > > ...
> > > > 	atomic_set();
> > > > does not magically become an atomic operation.
> > > 
> > > I just want the read and set are atomic, not the operations
> > > between atomic_read and atomic_set.
> > 
> > It makes no sense to use atomic operations here. atomic types are to
> > atomically read/modify/write variables. If all you ever do is
> > atomic_read and atomic_set then you can use a simple bool variable.
> > 
> 
> It is for ARM, but for other platforms, it may not.

It is for other platforms aswell. Otherwise the kernel would break into
pieces.

You only need atomic ops when you want to atomically read/modify/write a
variable.

Sascha


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