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 19:14:40 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...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 Sat, 30 Jan 2021 at 06:53, Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> 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?

According to the documentation I have, they must be enabled right
after enabling powering the chip and they must stay enabled all the
time.




-- 
With best wishes
Dmitry