[RFC PATCH] drivers: bus: add ARM CCI support

[Nicolas Pitre]

On Thu, 18 Apr 2013, Stephen Boyd wrote:

> On 04/11/13 07:47, Lorenzo Pieralisi wrote:
> > diff --git a/drivers/bus/arm-cci.c b/drivers/bus/arm-cci.c
> > new file mode 100644
> > index 0000000..81953de
> > --- /dev/null
> > +++ b/drivers/bus/arm-cci.c
> [...]
> > +static void notrace cci_port_control(unsigned int port, bool enable)
> > +{
> > +	void __iomem *base = ports[port].base;
> > +
> > +	if (!base)
> > +		return;
> > +
> > +	writel_relaxed(enable, base + CCI_PORT_CTRL);
> > +	while (readl_relaxed(cci_ctrl_base + CCI_CTRL_STATUS) & 0x1)
> > +			;
> 
> cpu_relax()?

In some cases there is no more cache coherence when this is called and 
the hardware might not be in a good state to cope with whatever action 
people might be tempted to insert into cpu_relax().  After the CCI is 
disabled it is important to keep a low profile and not touch anything 
global. With some early hardware revision, even a DMB here was harmful.


Nicolas