Hi Jason, On 01 May 2014 17:50, Jason wrote: > On Thu, May 01, 2014 at 09:50:56AM +0000, Phil Edworthy wrote: > > > > The logic should be: > > > if (bus == primary) > > > do io access to host bridge > > > else if (bus == secondary) > > > issue type 0 TLP on the wire > > > else if (bus > secondary && bus <= subordinate) > > > issue type 1 TLP on the wire > > > else > > > fail, invalid bus number > > > Where the three values come from the register in the PCI host bridge's > > > configuration space, and are kept in sync with the programming from > > > the Linux PCI core. > > > > > > It is just a happy hapenstance that root_bus_nr equals the value the > > > PCI core programmed into secondary - that is not guarenteed, you must > > > use the primary value directly. > > > For type0 TLPs, we are not checking that root_bus_nr equals the > > value the PCI core programmed into secondary, we are checking that > > the (root_bus_nr == bus->parent->number). The only way this wouldn't > > work is if root_bus_nr was not the root bus number. > > Okay, that isn't as sketchy, but that process still ignores the > subordinate bus number and the failure case as required by PCI. > > The goal here is to have the stuff below the drivers implement the PCI > spec so that the core code can assume everything below is > conformant. Drivers should not introduce gratuitous differences 'just > because' > > There is no reason drivers should be using PCI core structures to make > decisions when the spec says those decisions are driven by config > space fields. > > This way the PCI core code doesn't have to be aware of any weird > non-standard edge cases.. Such as not failing bus numbers beyond the > subordinate bus number. > > > Since the Synopsys DW driver also saves off sys->busnr and later > > uses this to determine if accesses are for the host bridge, I guess > > that means it won't always work either, right? Or is it ok because > > the DW driver saves sys->busnr in its .scan function? > > Sounds like it is making the same mistake, and nobody noticed. This is > another reason why it is important to implement correctly so people > copying copy the right stuff :) > > > When would the PCI core change the root bus number to something > > other than set in sys->busnr? > > I think the more likely scenario is that 'sys' in general is > architecture specific and its use is being discouraged so that host > drivers are not arch specific. > > A domain driver like rcar should always place the root complex > integrated bus as bus 0 in the domain. Ok, I now understand the reason for removing the dependency on sys->busnr. That makes sense & I'll update the driver for this. Thanks for your patience :) Phil -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
