Re: [RFC PATCH 07/16] PCI: Separate pci_host_bridge creation out of pci_create_root_bus()

[Liviu Dudau <Liviu.Dudau@arm.com>]

On Tue, Nov 18, 2014 at 08:32:26AM +0000, Yijing Wang wrote:
> 
> >> +LIST_HEAD(pci_host_bridge_list);
> >> +DECLARE_RWSEM(pci_host_bridge_sem);
> > 
> > Unless the pci_host_bridge_sem is accessed thousands of times per second,
> > it's normally better to use a simple mutex instead.
> 
> OK, I will use simple mutex instead.
> 
> > 
> >> +static struct resource busn_resource = {
> >> +	.name	= "PCI busn",
> >> +	.start	= 0,
> >> +	.end	= 255,
> >> +	.flags	= IORESOURCE_BUS,
> >> +};
> > 
> > I think it would be better to require callers to pass the bus resource
> > down to the function.
> 
> Hmm, I think most of caller will provide the bus resource, but some others
> will not give any bus resource, extremely, no any resources :(. But we still
> need properly configure their resources for compatibility.
> 
> > 
> >> +struct pci_host_bridge *pci_create_host_bridge(
> >> +		struct device *parent, u32 db, 
> >> +		struct pci_ops *ops, void *sysdata, 
> >> +		struct list_head *resources)
> >> +{
> > 
> > Do we still need to pass the 'sysdata' in here? If we are guaranteed to
> > have a device pointer, we should always be able to get the driver
> > private data from dev_get_drvdata(host->dev->parent).
> 
> We need, some platforms pass NULL pointer as host bridge parent.

Yijing,

May I suggest a different approach here? Rather than having to pass an opaque
pointer that gets converted by the host bridge driver back to the private
structure, what about promoting a new style of usage, that is similar to the
way device drivers work? Lets try to promote the embedding of the generic
pci_host_bridge structure in the host bridge specific structure! Then we can
access the private data doing container_of().

Something like this:

struct pci_controller {
	struct pci_host_bridge bridge;
	/* private host bridge data here */
	.....
};

#define PCI_CONTROLLER(bus)	({
	struct pci_host_bridge *hb = to_pci_host_bridge(bus->bridge); \
	container_of(hb, struct pci_controller, bridge); })


Then we can retrieve the host bridge structure from everywhere we have a device.

Best regards,
Liviu

> 
> > 
> >> +	host = kzalloc(sizeof(*host), GFP_KERNEL);
> >> +	if (!host)
> >> +		return NULL;
> > 
> > devm_kzalloc maybe?
> 
> I don't know much detail about devm_kzalloc(), but we have no pci host driver
> here, and I found no devm_kzalloc() uses in core PCI code before.
> 
> > 
> >> +	if (!resources) {
> >> +		/* Use default IO/MEM/BUS resources*/
> >> +		pci_add_resource(&host->windows, &ioport_resource);
> >> +		pci_add_resource(&host->windows, &iomem_resource);
> >> +		pci_add_resource(&host->windows, &busn_resource);
> >> +	} else {
> >> +		list_for_each_entry_safe(window, n, resources, list)
> >> +			list_move_tail(&window->list, &host->windows);
> >> +	}
> > 
> > I think we should assume that the correct resources are passed. You
> > could add a wrapper around this function to convert old platforms
> > though.
> 
> OK, I will move these code out of pci_create_host_bridge, and add a wrapper
> to setup the default resources.
> 
> > 
> >> +EXPORT_SYMBOL(pci_create_host_bridge);
> > 
> > EXPORT_SYMBOL_GPL() maybe?
> 
> OK, will update it.
> 
> > 
> >> diff --git a/include/linux/pci.h b/include/linux/pci.h
> >> index 8b11b38..daa7f40 100644
> >> --- a/include/linux/pci.h
> >> +++ b/include/linux/pci.h
> >> @@ -402,7 +402,12 @@ struct pci_host_bridge_window {
> >>  struct pci_host_bridge {
> >>  	struct device dev;
> >>  	struct pci_bus *bus;		/* root bus */
> >> +	struct list_head list;
> >>  	struct list_head windows;	/* pci_host_bridge_windows */
> >> +	int busnum;
> > 
> > The busnum should already be implied through the bus resource.
> 
> Yes, I will consider remove it and introduce a helper function to get the root bus number, thanks!
> 
> Thanks!
> Yijing.
> 
> > 
> > 	Arnd
> > 
> > .
> > 
> 
> 
> -- 
> Thanks!
> Yijing
> 
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