On Tue, Jan 16, 2024 at 08:02:58PM +0530, Vidya Sagar wrote: > The enumeration process leaves the 'Received Master Abort' bit set in > the Secondary Status Register of the downstream port in the following > scenarios. > > (1) The device connected to the downstream port has ARI capability > and that makes the kernel set the 'ARI Forwarding Enable' bit in > the Device Control 2 Register of the downstream port. This > effectively makes the downstream port forward the configuration > requests targeting the devices downstream of it, even though they > don't exist in reality. It causes the downstream devices return > completions with UR set in the status in turn causing 'Received > Master Abort' bit set. > > In contrast, if the downstream device doesn't have ARI capability, > the 'ARI Forwarding Enable' bit in the downstream port is not set > and any configuration requests targeting the downstream devices > that don't exist are terminated (section 6.13 of PCI Express Base > 6.0 spec) in the downstream port itself resulting in no change of > the 'Received Master Abort' bit. > > (2) A PCIe switch is connected to the downstream port and when the > enumeration flow tries to explore the presence of devices that > don't really exist downstream of the switch, the downstream > port receives the completions with UR set causing the 'Received > Master Abort' bit set. Are these the only possible ways this error is logged? I expected them to be logged when we enumerate below a Root Port that has nothing attached, for example. Does clearing them in pci_scan_bridge_extend() cover all ways this error might be logged during enumeration? I can't remember whether all enumeration goes through this path. > Clear 'Received Master Abort' bit to keep the bridge device in a clean > state post enumeration. > > Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx> > --- > V2: > * Changed commit message based on Bjorn's feedback > > drivers/pci/probe.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > index 795534589b98..640d2871b061 100644 > --- a/drivers/pci/probe.c > +++ b/drivers/pci/probe.c > @@ -1470,6 +1470,9 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev, > } > > out: > + /* Clear errors in the Secondary Status Register */ > + pci_write_config_word(dev, PCI_SEC_STATUS, 0xffff); > + > pci_write_config_word(dev, PCI_BRIDGE_CONTROL, bctl); > > pm_runtime_put(&dev->dev); > -- > 2.25.1 >
