On Wednesday 01 July 2020 16:34:42 Bjorn Helgaas wrote: > On Wed, Jul 01, 2020 at 10:20:44AM +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. > > > > This is just an optimization to prevent accessing PCIe registers when card > > is disconnected. Trying to access PCIe registers of disconnected card does > > not cause any crash, kernel just needs to wait for a timeout. So if card > > disappear immediately after checking for PCIe link (before accessing PCIe > > registers), it does not cause any problems. > > Thanks, this is good. I'd really like a short comment in the code as > well, because this sort of link-up check tends to get copied to new > drivers where it shouldn't be used, e.g., something like this: > > /* > * If the link goes down after we check for link-up, nothing bad > * happens but the config access times out. > */ Ok, it makes sense! I will send a new patch version. > > Signed-off-by: Pali Rohár <pali@xxxxxxxxxx> > > > > --- > > Changes in V2: > > * Update commit message, mention that this is optimization > > --- > > 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; > > + > > return true; > > } > > > > -- > > 2.20.1 > >
