linux-kernel - Re: [PATCH v2 3/5] pcie-qcom: provide a way to power up qca6390 chip on RB5 platform

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Date:   Sat, 30 Jan 2021 01:19:10 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Rob Herring <robh+dt@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Stanimir Varbanov <svarbanov@...sol.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v2 3/5] pcie-qcom: provide a way to power up qca6390 chip
 on RB5 platform

On Sat, 30 Jan 2021 at 00:50, Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Fri, Jan 29, 2021 at 06:45:21AM +0300, Dmitry Baryshkov wrote:
> > On 28/01/2021 22:26, Rob Herring wrote:
> > > On Thu, Jan 28, 2021 at 11:52 AM Dmitry Baryshkov
> > > <dmitry.baryshkov@...aro.org> wrote:
> > > >
> > > > Some Qualcomm platforms require to power up an external device before
> > > > probing the PCI bus. E.g. on RB5 platform the QCA6390 WiFi/BT chip needs
> > > > to be powered up before PCIe0 bus is probed. Add a quirk to the
> > > > respective PCIe root bridge to attach to the power domain if one is
> > > > required, so that the QCA chip is started before scanning the PCIe bus.
> > >
> > > This is solving a generic problem in a specific driver. It needs to be
> > > solved for any PCI host and any device.
> >
> > Ack. I see your point here.
> >
> > As this would require porting code from powerpc/spark of-pci code and
> > changing pcie port driver to apply power supply before bus probing happens,
> > I'd also ask for the comments from PCI maintainers. Will that solution be
> > acceptable to you?
>
> I can't say without seeing the code.  I don't know enough about this
> scenario to envision how it might look.
>
> I guess the QCA6390 is a PCIe device?  Why does it need to be powered
> up before probing?  Shouldn't we get a link-up interrupt when it is
> powered up so we could probe it then?

Not quite. QCA6390 is a multifunction device, with PCIe and serial
parts. It has internal power regulators which once enabled will
powerup the PCIe, serial and radio parts. There is no need to manage
regulators. Once enabled they will automatically handle device
suspend/resume, etc.

I'm not sure about link-up interrupt. I've just lightly tested using
PCIe HP on this port, getting no interrupts from it.
If I manually rescan the bus after enabling the qca6390 device (e.g.
via sysfs), it gets enabled, but then I see PCIe link errors (most
probably because the PCIe link was not retrained after the device
comes up).

> Nit: when changing any file, please take a look at the commit history
> and make yours match, e.g.,
>
>   pcie-qcom: provide a way to power up qca6390 chip on RB5 platform
>
> does not look like:

Ack.


-- 
With best wishes
Dmitry