Re: [PATCH v9 3/6] pci:host: Add Altera PCIe host controller driver

[Arnd Bergmann <arnd@arndb.de>]

On Wednesday 14 October 2015 17:28:45 Ley Foon Tan wrote:
> On Wed, Oct 14, 2015 at 5:09 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Wednesday 14 October 2015 16:32:25 Ley Foon Tan wrote:
> >> On Wed, Oct 14, 2015 at 4:20 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> >> > On Wednesday 14 October 2015 10:41:29 Ley Foon Tan wrote:
> >> >> +static int altera_pcie_remove(struct platform_device *pdev)
> >> >> +{
> >> >> +     struct altera_pcie *pcie = platform_get_drvdata(pdev);
> >> >> +
> >> >> +     altera_pcie_free_irq_domain(pcie);
> >> >> +     platform_set_drvdata(pdev, NULL);
> >> >> +     return 0;
> >> >> +}
> >> >
> >> > I just noticed this. Does it actually work to unload the module
> >> > and tear down all the pci_dev structures in a safe way?
> >> Good catch. It only can be compiled as builtin-moduley now, so we can
> >> remove this _remove callback function.
> >
> > I think we should change both: make it possible to load the
> > driver dynamically, and remove the altera_pcie_remove function.
> This driver depends on the pci fixups to work correctly. But, fixups
> callback functions in this driver are not being call if the driver is
> loadable module.

Ah, I see. We should find a better way to deal with this, as we
are getting an increasing number of host driver specific fixups.

Bjorn, do you have any idea here?

Could we perhaps have a helper function that lets us register
fixups dynamically?

> The linker script keeps all pci fixup callbacks in pci fixup regions
> during kernel compile time. So, it needs to be builtin module. Do you
> know any way we can update those fixup regions?

The only method I'm aware of at the moment is move the fixups to
drivers/pci/quirks.c and enclose them in an #ifdef if you want them
to not appear in kernels that don't support your SoC.

> > You can prevent the module from being unloaded if you also remove
> > the module_platform_driver() directive and add a module_init()
> > without a matching module_exit().
> >
> > Please also add a '.suppress_bind_attrs = true,' flag in the driver
> > struct to prevent manual unbinding.
> I think we don't need these if it only can work as builtin module.

No, this is orthogonal, you need it either way, as built-in drivers
can still be unbound by writing to sysfs. Try writing the device name
to /sys/bus/platform/drivers/altera-pcie/unbind and watch it blow up ;-)

	Arnd