On Mon, Jul 18, 2022 at 2:14 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> On Sat, Jul 16, 2022 at 06:24:49PM -0400, Jim Quinlan wrote:
> > Currently, the function does the setup for establishing PCIe link-up
> > with the downstream device, and it does the actual link-up as well.
> > The calling sequence is (roughly) the following in the probe:
> >
> > -> brcm_pcie_probe()
> > -> brcm_pcie_setup(); /* Set-up and link-up */
> > -> pci_host_probe(bridge);
> >
> > This commit splits the setup function in two: brcm_pcie_setup(), which only
> > does the set-up, and brcm_pcie_start_link(), which only does the link-up.
> > The reason why we are doing this is to lay a foundation for subsequent
> > commits so that we can turn on any power regulators, as described in the
> > root port's DT node, prior to doing link-up.
>
> All drivers that care about power regulators turn them on before
> link-up, but typically those regulators are described directly under
> the host bridge itself.
Hi Bjorn,
Actually, what you describe is what I proposed with my v1 back in Nov 2020.
The binding commit message said,
"Quite similar to the regulator bindings found in "rockchip-pcie-host.txt",
this allows optional regulators to be attached and controlled by the
PCIe RC driver."
>
> IIUC the difference here is that you have regulators described under
> Root Ports (not the host bridge/Root Complex itself), so you don't
> know about them until you've enumerated the Root Ports.
> brcm_pcie_probe() can't turn them on directly because it doesn't know
> what Root Ports are present and doesn't know about regulators below
> them.
The reviewer's requested me to move the regulator node(s) elsewhere,
and at some point later it was requested to be placed under the Root Port
driver. I would love to return them under the host bridge, just say the word!
>
> So I think brcm_pcie_setup() does initialization that doesn't depend
> on the link or any downstream devices, and brcm_pcie_start_link() does
> things that depend on the link being up. Right?
Yes.
>
> If so, "start_link" might be a slight misnomer since AFAICT
> brcm_pcie_start_link() doesn't do anything to initiate link-up except
> maybe deasserting fundamental reset. Some drivers start the LTSSM or
> explicitly enable link training, but brcm_pcie_start_link() doesn't
> seem to do anything like that.
>
> brcm_pcie_start_link() still does brcm_pcie_set_outbound_win(). Does
> that really depend on the link being up? If that only affects the
> Root Port, maybe it could be done before link-up?
Some of the registers cannot be accessed until after linkup but these do
not have that issue. I will change this.
Jim Quinlan
Broadcom STB
>
> > We do this by defining an
> > add_bus() callback which is invoked during enumeraion. At the end of this
> > patchset the probe function trace will look something like this:
> >
> > -> brcm_pcie_probe()
> > -> brcm_pcie_setup(); /* Set-up only */
> > -> pci_host_probe(bridge);
> > -> [enumeration]
> > -> pci_alloc_child_bus()
> > -> bus->ops->add_bus(bus); /* We've set this op */
> > -> brcm_pcie_add_bus() /* Our callback */
> > -> [turn on regulators] /* Main objective! */
> > -> brcm_pcie_start_link() /* Link-up */
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