On Tue, Dec 8, 2015 at 2:31 PM, Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx> wrote: > > On 12/03/2015 03:35 PM, Stanimir Varbanov wrote: > > Add 'write memory' barrier after enable region in PCIE_ATU_CR2 > > register. The barrier is needed to ensure that the region enable > > request has been reached it's destination at time when we > > read/write to PCI configuration space. > > > > Without this barrier PCI device enumeration during kernel boot > > is not reliable, and reading configuration space for particular > > PCI device on the bus returns zero aka no device. > > Anand, Jingoo, what is your opinion? > > > > > Signed-off-by: Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx> > > --- > > drivers/pci/host/pcie-designware.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/drivers/pci/host/pcie-designware.c b/drivers/pci/host/pcie-designware.c > > index 02a7452bdf23..ed4dc2e2553b 100644 > > --- a/drivers/pci/host/pcie-designware.c > > +++ b/drivers/pci/host/pcie-designware.c > > @@ -164,6 +164,11 @@ static void dw_pcie_prog_outbound_atu(struct pcie_port *pp, int index, > > dw_pcie_writel_rc(pp, upper_32_bits(pci_addr), PCIE_ATU_UPPER_TARGET); > > dw_pcie_writel_rc(pp, type, PCIE_ATU_CR1); > > dw_pcie_writel_rc(pp, PCIE_ATU_ENABLE, PCIE_ATU_CR2); > > + /* > > + * ensure that the ATU enable has been happaned before accessing > > + * pci configuration/io spaces through dw_pcie_cfg_[read|write]. > > + */ > > + wmb(); > > } > > My understnading is that since writel() of dw_pcie_writel_rc() in above code and readl(), writel() of dw_pcie_cfg_[read|write]() (which will follow) goes through same device (ie PCIe host here). So, it is guaranteed that 1st writel() will be executed before later readl()/writel(). If that is true then we do not need any explicit barrier here. Arnd, Russel: whats your opinion here. ~Pratyush -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
