| Message ID | 20240210-topic-8280_pcie-v2-2-1cef4b606883@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | Qualcomm PCIe RC shutdown & reinit | expand |
Maybe include the reason in the subject? "Read back" is literally what the diff says. On Sat, Feb 10, 2024 at 06:10:06PM +0100, Konrad Dybcio wrote: > To ensure write completion, read the PARF_LTSSM register after setting > the LTSSM enable bit before polling for "link up". The write will obviously complete *some* time; I assume the point is that it's important for it to complete before some other event, and it would be nice to know why that's important. > Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> > Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org> > --- > drivers/pci/controller/dwc/pcie-qcom.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c > index cbde9effa352..6a469ed213ce 100644 > --- a/drivers/pci/controller/dwc/pcie-qcom.c > +++ b/drivers/pci/controller/dwc/pcie-qcom.c > @@ -539,6 +539,7 @@ static void qcom_pcie_2_3_2_ltssm_enable(struct qcom_pcie *pcie) > val = readl(pcie->parf + PARF_LTSSM); > val |= LTSSM_EN; > writel(val, pcie->parf + PARF_LTSSM); > + readl(pcie->parf + PARF_LTSSM); > } > > static int qcom_pcie_get_resources_2_3_2(struct qcom_pcie *pcie) > > -- > 2.40.1 >
On 12.02.2024 22:17, Bjorn Helgaas wrote: > Maybe include the reason in the subject? "Read back" is literally > what the diff says. > > On Sat, Feb 10, 2024 at 06:10:06PM +0100, Konrad Dybcio wrote: >> To ensure write completion, read the PARF_LTSSM register after setting >> the LTSSM enable bit before polling for "link up". > > The write will obviously complete *some* time; I assume the point is > that it's important for it to complete before some other event, and it > would be nice to know why that's important. Right, that's very much meaningful on non-total-store-ordering architectures, like arm64, where the CPU receives a store instruction, but that does not necessarily impact the memory/MMIO state immediately. Konrad
diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c index cbde9effa352..6a469ed213ce 100644 --- a/drivers/pci/controller/dwc/pcie-qcom.c +++ b/drivers/pci/controller/dwc/pcie-qcom.c @@ -539,6 +539,7 @@ static void qcom_pcie_2_3_2_ltssm_enable(struct qcom_pcie *pcie) val = readl(pcie->parf + PARF_LTSSM); val |= LTSSM_EN; writel(val, pcie->parf + PARF_LTSSM); + readl(pcie->parf + PARF_LTSSM); } static int qcom_pcie_get_resources_2_3_2(struct qcom_pcie *pcie)