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SubjectRe: [PATCH v2] PCI: aardvark: Don't touch PCIe registers if no card connected
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@kernel.org>
> >
> > ---
> > 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
> >

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