On Thu, Jul 21, 2022 at 10:53:54AM -0400, Jim Quinlan wrote: > https://lore.kernel.org/linux-pci/20171215201434.GY30595@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > On Wed, Jul 20, 2022 at 6:06 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > On Sat, Jul 16, 2022 at 06:24:50PM -0400, Jim Quinlan wrote: > > > Our PCIe RC HW has an atypical behavior: if it does not have PCIe link > > > established between itself and downstream, any subsequent config space > > > access causes a CPU abort. This commit sets a "refusal mode" if the PCIe > > > link-up fails, and this has our pci_ops map_bus function returning a NULL > > > address, which in turn precludes the access from happening. > > > > > > Right now, "refusal mode" is window dressing. It will become relevant > > > in a future commit when brcm_pcie_start_link() is invoked during > > > enumeration instead of before it. > > > > > > Signed-off-by: Jim Quinlan <jim2101024@xxxxxxxxx> > > > --- > > > drivers/pci/controller/pcie-brcmstb.c | 24 ++++++++++++++++++++++++ > > > 1 file changed, 24 insertions(+) > > > > > > diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c > > > index c026446d5830..72219a4f3964 100644 > > > --- a/drivers/pci/controller/pcie-brcmstb.c > > > +++ b/drivers/pci/controller/pcie-brcmstb.c > > > @@ -255,6 +255,7 @@ struct brcm_pcie { > > > u32 hw_rev; > > > void (*perst_set)(struct brcm_pcie *pcie, u32 val); > > > void (*bridge_sw_init_set)(struct brcm_pcie *pcie, u32 val); > > > + bool refusal_mode; > > > }; > > > > > > static inline bool is_bmips(const struct brcm_pcie *pcie) > > > @@ -687,6 +688,19 @@ static void __iomem *brcm_pcie_map_conf(struct pci_bus *bus, unsigned int devfn, > > > if (pci_is_root_bus(bus)) > > > return PCI_SLOT(devfn) ? NULL : base + where; > > > > > > + if (pcie->refusal_mode) { > > > + /* > > > + * At this point we do not have PCIe link-up. If there is > > > + * a config read or write access besides those targeting > > > + * the host bridge, our PCIe HW throws a CPU abort. To > > > + * prevent this we return the NULL address. The calling > > > + * functions -- pci_generic_config_*() -- will notice this > > > + * and not perform the access, and if it is a read access, > > > + * 0xffffffff is returned. > > > + */ > > > + return NULL; > > > + } > > > > Is this any different from all the other .map_bus() implementations > > that return NULL when the link is down? > > Not really, but long ago I submitted code that gated the config spec > access based on link status and was advised not to do it [1]. > I'll be happy to make it look like the others. > > [1] https://lore.kernel.org/linux-pci/20171215201434.GY30595@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ My point there was that if you can deal with the abort cleanly, that's the best approach. Apparently brcmstb can't recover cleanly, so you have to settle for the 99% solution. The refusal_mode approach has the same race as checking *_pcie_link_up(), since the link may go down between the time brcm_pcie_start_link() sees that it is up and the time somebody does a config access: brcm_pcie_start_link pcie->refusal_mode = false <link goes down> brcm_pcie_map_conf if (pcie->refusal_mode) # still false <config access causes abort> So there's no advantage in making the code look different. Checking for link-up in the config access path can never completely remove the window, but it does make it smaller than using refusal_mode. Bjorn
