Re: [PATCH v10 4/6] PCI: hisi: Add PCIe host support for HiSilicon SoC Hip05

[Arnd Bergmann <arnd@arndb.de>]

On Tuesday 13 October 2015 06:58:42 Gabriele Paoloni wrote:
> 
> > >> +
> > >> +static int __init hisi_pcie_init(void)
> > >> +{
> > >> +	return platform_driver_probe(&hisi_pcie_driver, hisi_pcie_probe);
> > >> +}
> > >> +subsys_initcall(hisi_pcie_init);
> > >
> > > Can you use module_platform_driver() or module_platform_driver_probe()
> > > here instead of the subsys_initcall()?  No, I don't really know what
> > > the difference between module_platform_driver() and
> > > module_platform_driver_probe() is, sorry :)

module_platform_driver_probe() will only call the probe function once
(and fail in case of -EPROBE_DEFER), while module_platform_driver()
installs the platform driver in a way that the device can be bound
and unbound at any point.

> > In fact, I used module_platform_driver_probe in previous version, but
> > A PCIe VGA card of HiSilicon will use Hip05 PCIe host, so we modified
> > module_platform_driver_probe to subsys_initcall which will be called
> > before module_platform_driver_probe.
> > 
> > We will upstream the driver of above PCIe VGA card soon.

I don't see a reason why a VGA driver would need the PCI host to be
probed this early, unless it is the only usable console in the system.

> Hi Bjorn, firstly many thanks for looking at this.
> 
> About this last bit the reason why we use subsys_initcall() is that
> our host bridge is embedded in the SoC and as such is not hot-pluggable
> for instance see:
> http://lxr.free-electrons.com/source/Documentation/driver-model/platform.txt#L59

We should still be able to build the driver as a loadable module,
even if you don't do that on your own kernels. 

This doesn't mean that it has to be module_platform_driver, subsys_initcall
will also work in a loadable module, it just won't be as early. However,
we should try to come up with a consistent approach for all PCI host drivers,
I don't see any reason for hisi to be different from the others here.

> Our approach is also used by Exynos:
> http://lxr.free-electrons.com/source/drivers/pci/host/pci-exynos.c#L644

Maybe we should change that too.

	Arnd