linux-kernel - Re: [PATCH v2 2/6] PCI: brcmstb: Split brcm_pcie

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Message-ID: <CA+-6iNz8DTjAMXnWuOd=0W=qa6J4uD03oH3RJezEk1WxaUN1NA@mail.gmail.com>
Date:   Tue, 19 Jul 2022 09:08:48 -0400
From:   Jim Quinlan <james.quinlan@...adcom.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Jim Quinlan <jim2101024@...il.com>,
        "open list:PCI NATIVE HOST BRIDGE AND ENDPOINT DRIVERS" 
        <linux-pci@...r.kernel.org>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Cyril Brulebois <kibi@...ian.org>,
        "maintainer:BROADCOM BCM7XXX ARM ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/6] PCI: brcmstb: Split brcm_pcie_setup() into two funcs

On Mon, Jul 18, 2022 at 6:40 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Mon, Jul 18, 2022 at 02:56:03PM -0400, Jim Quinlan wrote:
> > On Mon, Jul 18, 2022 at 2:14 PM Bjorn Helgaas <helgaas@...nel.org> 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.
> >
> > 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!
>
> Actually, I think my understanding is wrong.  Even though the PCI core
> hasn't enumerated the Root Port as a pci_dev, brcm_pcie_setup() knows
> about it and should be able to look up the regulators and turn them
> on.


One can do this with
        regulator_bulk_get(NULL, ...);

However, MarkB did not like the idea of a driver getting the regulator from
the global DT namespace [1].

For the RC driver, one  cannot invoke  regulator_bulk_get(dev, ...) if
there is not a
direct child regulator node.  One needs to use the Port driver device.
The Port driver
device does not exist at this point unless one tries to prematurely create it;
I tried this and it was a mess to say the least.

>
> Can you dig up the previous discussion about why the regulators need
> to be under the Root Port and why they can't be turned on before
> calling pci_host_probe()?


RobH did not want the regulators to be under the RC as he said their DT
location should resemble the HW [2].  The consensus evolved
to place it under the port driver, which can provide a general
mechanism for turning
on regulators anywhere in the PCIe tree.

Regards,
Jim Quinlan
Broadcom STB

[1] https://lore.kernel.org/linux-pci/20210329162539.GG5166@sirena.org.uk/
[2] https://lore.kernel.org/linux-pci/CAL_JsqKPKk3cPO8DG3FQVSHrKnO+Zed1R=PV7n7iAC+qJKgHcw@mail.gmail.com/


>
>
> Bjorn

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