On 2021/7/27 6:05, Bjorn Helgaas wrote: > On Wed, Feb 24, 2021 at 05:47:58PM +0800, Yicong Yang wrote: >> On 2021/2/3 20:53, Yicong Yang wrote: >>> Per Downstream Port Containment Related Enhancements ECN[1] >>> Table 4-6, Interpretation of _OSC Control Field Returned Value, >>> for bit 7 of _OSC control return value: >>> >>> "Firmware sets this bit to 1 to grant the OS control over PCI Express >>> Downstream Port Containment configuration." >>> "If control of this feature was requested and denied, >>> or was not requested, the firmware returns this bit set to 0." >>> >>> We store bit 7 of _OSC control return value in host->native_dpc, >>> check it before enable the dpc service as the firmware may not >>> grant the control. >>> >>> [1] Downstream Port Containment Related Enhancements ECN, >>> Jan 28, 2019, affecting PCI Firmware Specification, Rev. 3.2 >>> https://members.pcisig.com/wg/PCI-SIG/document/12888 >>> >>> Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx> >>> --- >>> Change since v1: >>> - use correct reference for _OSC control return value >>> >>> drivers/pci/pcie/portdrv_core.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c >>> index e1fed664..7445d03 100644 >>> --- a/drivers/pci/pcie/portdrv_core.c >>> +++ b/drivers/pci/pcie/portdrv_core.c >>> @@ -253,7 +253,8 @@ static int get_port_device_capability(struct pci_dev *dev) >>> */ >>> if (pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DPC) && >>> pci_aer_available() && >>> - (pcie_ports_dpc_native || (services & PCIE_PORT_SERVICE_AER))) >>> + (pcie_ports_dpc_native || >>> + ((services & PCIE_PORT_SERVICE_AER) && host->native_dpc))) >>> services |= PCIE_PORT_SERVICE_DPC; >>> >> >> the check here maybe problematic. the bit 7 of _OSC return value is reserved >> previously and the change here may break the backward compatibility. >> currently we make dpc enabled along with aer, which can ensure the native >> dpc won't be enabled if the edr is enabled. > > Since you think this is problematic, I'll drop it for now. If you > decide it's the right thing to do, please post it again. > yes, I still think this has problem. sorry for the noise. >> i feel a bit confused as the bit 7 is not used. >> does it provide a way to enable native dpc regardless of aer ownership? >> just as pcie_ports=dpc-native does when i checked the discussion in [1]. >> >> [1] https://lore.kernel.org/linux-pci/20191023192205.97024-1-olof@xxxxxxxxx/ >> >> Thanks, >> Yicong >> >>> if (pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM || >>> >> > > . >
