On Tue, Jun 30, 2020 at 04:04:20PM +0200, Pali Rohár wrote: > On Tuesday 30 June 2020 08:51:27 Bjorn Helgaas wrote: > > On Thu, May 28, 2020 at 06:38:09PM +0200, Pali Rohár wrote: > > > On Thursday 28 May 2020 11:26:04 Bjorn Helgaas wrote: > > > > On Thu, May 28, 2020 at 04:31:41PM +0200, Pali Rohár wrote: > > > > > When there is no PCIe card connected and advk_pcie_rd_conf() or > > > > > advk_pcie_wr_conf() is called for PCI bus which doesn't belong to emulated > > > > > root bridge, the aardvark driver throws the following error message: > > > > > > > > > > advk-pcie d0070000.pcie: config read/write timed out > > > > > > > > > > Obviously accessing PCIe registers of disconnected card is not possible. > > > > > > > > > > Extend check in advk_pcie_valid_device() function for validating > > > > > availability of PCIe bus. If PCIe link is down, then the device is marked > > > > > as Not Found and the driver does not try to access these registers. > > > > > > > > > > Signed-off-by: Pali Rohár <pali@xxxxxxxxxx> > > > > > --- > > > > > drivers/pci/controller/pci-aardvark.c | 3 +++ > > > > > 1 file changed, 3 insertions(+) > > > > > > > > > > diff --git a/drivers/pci/controller/pci-aardvark.c b/drivers/pci/controller/pci-aardvark.c > > > > > index 90ff291c24f0..53a4cfd7d377 100644 > > > > > --- a/drivers/pci/controller/pci-aardvark.c > > > > > +++ b/drivers/pci/controller/pci-aardvark.c > > > > > @@ -644,6 +644,9 @@ static bool advk_pcie_valid_device(struct advk_pcie *pcie, struct pci_bus *bus, > > > > > if ((bus->number == pcie->root_bus_nr) && PCI_SLOT(devfn) != 0) > > > > > return false; > > > > > > > > > > + if (bus->number != pcie->root_bus_nr && !advk_pcie_link_up(pcie)) > > > > > + return false; > > > > > > > > I don't think this is the right fix. This makes it racy because the > > > > link may go down after we call advk_pcie_valid_device() but before we > > > > perform the config read. > > > > > > Yes, it is racy, but I do not think it cause problems. Trying to read > > > PCIe registers when device is not connected cause just those timeouts, > > > printing error message and increased delay in advk_pcie_wait_pio() due > > > to polling loop. This patch reduce unnecessary access to PCIe registers > > > when advk_pcie_wait_pio() polling just fail. > > > > What happens when the device is removed after advk_pcie_link_up() > > returns true, but before we actually do the config access? > > Do you mean to remove device physically at runtime? I was told that our > board would crash or issue reset. Removing device from mini PCIe slot > without power off is not supported. Right, I don't think PCIe mini cards support hotplug. > Anyway, currently we are trying to read from device registers even when > no device is connected. So when advk_pcie_link_up() returns true and > after that device is not connected (somehow board and kernel would be > still alive) I guess that it would behave as without applying this > patch. So kernel starts reading from register and would wait until > timeout expires. As device is not connected there would be no answer, > so kernel print error message to dmesg (same as in commit message) and > returns error that read failed. OK, so if I understand correctly, checking advk_pcie_link_up() is strictly an optimization. If we guess wrong (e.g., after calling advk_pcie_link_up(), the link went down because the card was removed, DPC triggered, etc), the only bad thing is that we wait for a timeout; it never causes a crash. If that's the case, I'm fine with this. But please add a comment to that effect. I think several other drivers check for the link being up because we actually crash if we try to read config space when the link is down. That's what I was trying to avoid here. Bjorn
