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

[Lorenzo Pieralisi]

Thanks for the review Stephen.

On Thu, Apr 18, 2013 at 06:20:48PM +0100, 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()?

Nico explained the reason why I did not add a cpu_relax() here, actually
having this function in C is already a moot point.

> > +}
> [...]
> > +int notrace __cci_control_port_by_device(struct device_node *np, bool enable)
> > +{
> > +	int port = cci_ace_lite_port(np);
> > +	if (WARN_ONCE(port < 0,
> > +		      "ACE lite port look-up failure, node %p\n", np))
> > +		return -ENODEV;
> > +	cci_port_control(port, enable);
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(__cci_control_port_by_device);
> > +
> > +static const struct of_device_id arm_cci_matches[];
> 
> Why not just put the definition here then?

Bah, absolutely.

> > +
> > +static int __init cci_driver_probe(struct platform_device *pdev)
> 
> You probably want to drop the __init considering device hotplug is not
> optional anymore.

I will rework the driver to make it non-hotpluggable compliant (ie use
platform_driver_probe()) honestly hotplug should be strictly prohibited
for CCI, it is a bus tied to CPU clusters I can hardly see any reason to
allow that.

> > +{
> > +	const struct of_device_id *match;
> > +	struct cci_nb_ports const *cci_config;
> > +	int ret, j, i, nb_ace = 0, nb_ace_lite = 0;
> > +	struct device_node *np, *cp;
> > +	const char *match_str;
> > +
> > +	match = of_match_device(arm_cci_matches, &pdev->dev);
> > +
> > +	if (!match)
> > +		return -ENODEV;
> 
> It would be nice if we could get the data field from the of_device_id
> without doing the search again. Can we update the of_platform code to
> assign some field that you can get from the platform device?

I guess there is a reason why it has not been implemented, I will have
a look to check that though.

> > +
> > +	cci_config = (struct cci_nb_ports const *)match->data;
> > +	nb_cci_ports = cci_config->nb_ace + cci_config->nb_ace_lite;
> > +	ports = kzalloc(sizeof(*ports) * nb_cci_ports, GFP_KERNEL);
> 
> kcalloc()?

Absolutely.

> > +	if (!ports)
> > +		return -ENOMEM;
> > +
> > +	np = pdev->dev.of_node;
> > +	cci_ctrl_base = of_iomap(np, 0);
> 
> This is a platform driver so we should use non-of functions to map,
> platform_get_resource()/ioremap(), etc.

Well, it has a strict dependency on DT though. Point taken anyway, I
will think about this.

> > +}
> > +
> > +static int __exit cci_driver_remove(struct platform_device *pdev)
> > +{
> 
> You probably want to drop the __exit here too.

See above.

> > diff --git a/include/linux/arm-cci.h b/include/linux/arm-cci.h
> > new file mode 100644
> > index 0000000..e9514a2
> > --- /dev/null
> > +++ b/include/linux/arm-cci.h
> > @@ -0,0 +1,44 @@
> > +
> > +#ifndef __LINUX_ARM_CCI_H
> > +#define __LINUX_ARM_CCI_H
> > +
> > +#include <linux/errno.h>
> > +#include <linux/of.h>
> > +#include <linux/types.h>
> 
> You can declare
> 
> struct device_node;
> 
> here to avoid including linux/of.h. Less includes means less circular
> dependencies.

Ok.

Thanks,
Lorenzo