Re: [PATCH 2/4] PCI: designware: get rid of pci_scan_root_bus

[Jingoo Han <jg1.han@samsung.com>]

On Thursday, July 24, 2014 5:32 PM, Lucas Stach wrote:
> Am Donnerstag, den 24.07.2014, 13:11 +0900 schrieb Jingoo Han:
> > On Thursday, July 24, 2014 2:53 AM, Lucas Stach wrote:
> > >
> > > Use pci_create_root_bus() similar to other pci
> > > host controller drivers.
> > >
> > > The main problem with pci_scan_root_bus() is that
> > > not only it will create the root bus, but also try
> > > to activate all devices on the bus. This triggers
> > > PCI device drivers probe, which try to use the device
> > > but fail as resource allocation isn't done at that
> > > point in time.
> > >
> > > To work around this we made sure that the host
> > > controller driver is probed early and finishes resource
> > > allocation before any other device drivers are registered.
> > > Switching to pci_create_root_bus() allows us to get rid
> > > of this special handling.
> > >
> > > Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> > > ---
> > >  drivers/pci/host/pcie-designware.c | 15 +++++++--------
> > >  1 file changed, 7 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/drivers/pci/host/pcie-designware.c b/drivers/pci/host/pcie-designware.c
> > > index b13a830c8b0f..b869e202367c 100644
> > > --- a/drivers/pci/host/pcie-designware.c
> > > +++ b/drivers/pci/host/pcie-designware.c
> > > @@ -801,14 +801,13 @@ static struct pci_bus *dw_pcie_scan_bus(int nr, struct pci_sys_data *sys)
> > >  	struct pci_bus *bus;
> > >  	struct pcie_port *pp = sys_to_pcie(sys);
> > >
> > > -	if (pp) {
> > > -		pp->root_bus_nr = sys->busnr;
> > > -		bus = pci_scan_root_bus(pp->dev, sys->busnr, &dw_pcie_ops,
> > > -					sys, &sys->resources);
> > > -	} else {
> > > -		bus = NULL;
> > > -		BUG();
> > > -	}
> > > +	pp->root_bus_nr = sys->busnr;
> > > +	bus = pci_create_root_bus(pp->dev, sys->busnr,
> > > +				  &dw_pcie_ops, sys, &sys->resources);
> > > +	if (!bus)
> > > +		return NULL;
> > > +
> > > +	pci_scan_child_bus(bus);
> >
> >
> > I think that we still need to check if pp is NULL.
> > Then, how about adding NULL check as below?
> >
> No I don't think it's needed as it doesn't provide any additional
> security.
> 
> The only code path that is calling this dw_pci_scan_bus() is in
> pcibios_init_hw() which always fills sys->private_data with
> hw_pci->private_data. As we are always filling hw_pci->private_data with
> a pointer to our pcie_port structure in dw_pcie_host_init() the only way
> for pp to be NULL at this point would be for pp to be NULL in
> dw_pcie_host_init(). This would obviously crash a lot earlier.
> 
> So this check is just adding to LOC without adding any value.

Hi Lucas,

I see what you mean. However, pcie-designware.c has been handled by
various engineers. So, it is not sure that the current sequence will
not change in the future. Anyway, thank you for your comment. :-)

Best regards,
Jingoo Han

> 
> Regards,
> Lucas
> 
> --
> Pengutronix e.K.             | Lucas Stach                 |
> Industrial Linux Solutions   | http://www.pengutronix.de/  |