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

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Sat 30 Jan 10:14 CST 2021, Dmitry Baryshkov wrote:

> On Sat, 30 Jan 2021 at 06:53, Bjorn Andersson
> <bjorn.andersson@linaro.org> wrote:
> >
> > On Fri 29 Jan 16:19 CST 2021, Dmitry Baryshkov wrote:
> >
> > > On Sat, 30 Jan 2021 at 00:50, Bjorn Helgaas <helgaas@kernel.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@linaro.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.
> 

So presumably just marking these things always-on and flipping the GPIO
statically won't be good enough due to the lack of control over the
timing.

This really do look like a simplified case of what we see with the
PCIe attached modems, where similar requirements are provided, but also
the ability to perform a device specific reset sequence in case the
hardware has locked up. I'm slightly worried about the ability of
extending your power-domain model to handle the restart operation
though.

Regards,
Bjorn