Re: [PATCH v2 2/3] PCI: dwc: Add Qualcomm PCIe Endpoint controller driver

On Tue 15 Jun 16:40 CDT 2021, Rob Herring wrote:

On Sat, Jun 5, 2021 at 9:07 PM Bjorn Andersson
[off-list ref] wrote:

quoted

On Thu 03 Jun 05:38 CDT 2021, Manivannan Sadhasivam wrote:

quoted

Add driver support for Qualcomm PCIe Endpoint controller driver based on
the Designware core with added Qualcomm specific wrapper around the
core. The driver support is very basic such that it supports only
enumeration, PCIe read/write, and MSI. There is no ASPM and PM support
for now but these will be added later.

The driver is capable of using the PERST# and WAKE# side-band GPIOs for
operation and written on top of the DWC PCI framework.

Co-developed-by: Siddartha Mohanadoss <redacted>
Signed-off-by: Siddartha Mohanadoss <redacted>
[mani: restructured the driver and fixed several bugs for upstream]
Signed-off-by: Manivannan Sadhasivam <redacted>

Really nice to see this working!

[...]

quoted

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+static void qcom_pcie_ep_configure_tcsr(struct qcom_pcie_ep *pcie_ep)
+{
+     writel_relaxed(0x0, pcie_ep->tcsr + TCSR_PCIE_PERST_EN);

Please avoid _relaxed accessor unless there's a strong reason, and if so
document it.

Uhhh, what!? That's the wrong way around from what I've ever seen
anyone say. Have you ever looked at the resulting code on arm32 with
OMAP enabled? It's just a memory barrier and an indirect function call
on every access.

Use readl/writel if you have an ordering requirement WRT DMA,
otherwise use relaxed variants.

That does make sense. Unfortunately I don't know where this started, but
I would guess it might have been a reaction to the fact that people
where just sprinkling wmb() all over the place to be on the safe side...

quoted

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+     writel_relaxed(0x0, pcie_ep->tcsr + TCSR_PERST_SEPARATION_ENABLE);
+}
+

[...]

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+static struct platform_driver qcom_pcie_ep_driver = {
+     .probe  = qcom_pcie_ep_probe,
+     .driver = {
+             .name           = "qcom-pcie-ep",

Skip the indentation of the '='.

quoted

+             .suppress_bind_attrs = true,

Why do we suppress_bind_attrs?

Because remove is not handled.

Not handled in Mani's driver, or is this a PCI thing?

Regards,
Bjorn