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:   Fri, 29 Jan 2021 21:53:12 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.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 Fri 29 Jan 16:19 CST 2021, Dmitry Baryshkov wrote:

> 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.
> 

So what you're saying is that if either the PCI controller or bluetooth
driver probes these regulators will be turned on, indefinitely?

If so, why do we need a driver to turn them on, rather than just mark
them as always-on?

What's the timing requirement wrt regulators vs WL_EN/BT_EN?

Regards,
Bjorn A

> 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