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

On Tue 02 Feb 15:37 CST 2021, Rob Herring wrote:

On Tue, Feb 2, 2021 at 1:48 PM Bjorn Andersson
[off-list ref] wrote:

quoted

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

quoted

On Sat, 30 Jan 2021 at 06:53, Bjorn Andersson
[off-list ref] wrote:

quoted

On Fri 29 Jan 16:19 CST 2021, Dmitry Baryshkov wrote:

quoted

On Sat, 30 Jan 2021 at 00:50, Bjorn Helgaas [off-list ref] wrote:

quoted

On Fri, Jan 29, 2021 at 06:45:21AM +0300, Dmitry Baryshkov wrote:

quoted

On 28/01/2021 22:26, Rob Herring wrote:

quoted

On Thu, Jan 28, 2021 at 11:52 AM Dmitry Baryshkov
[off-list ref] wrote:

quoted

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.

I think this is an abuse of 'power-domains'. Just define the
regulators in both WiFi and BT nodes and have each driver enable them.
They're refcounted. If that's still not enough control over the power
sequencing, then create a 3rd entity to do it, but that doesn't need
to leak into DT. You already have all the information you need.

As Dmitry explained he still need to pull the two GPIOs high after
enabling the regulators, but before scanning the PCI or serdev buses.

I was thinking something along the lines you suggest, but I've not been
able to come up with something that will guarantee the ordering of the
events.

Regards,
Bjorn