Hi,

On Thu, 8 Jul 2021 at 13:10, Ulf Hansson [off-list ref] wrote:

- Peter (the email was bouncing)

+ Peter's kernel.org address

On Tue, 6 Jul 2021 at 13:55, Mark Brown [off-list ref] wrote:

quoted

On Tue, Jul 06, 2021 at 09:54:03AM +0200, Ulf Hansson wrote:

quoted

On Tue, 22 Jun 2021 at 00:32, Dmitry Baryshkov

quoted

quoted

Qualcomm QCA6390/1 is a family of WiFi + Bluetooth SoCs, with BT part
being controlled through the UART and WiFi being present on PCIe
bus. Both blocks share common power sources. Add device driver handling
power sequencing of QCA6390/1.

quoted

Power sequencing of discoverable buses have been discussed several
times before at LKML. The last attempt [1] I am aware of, was in 2017
from Peter Chen. I don't think there is a common solution, yet.

This feels a bit different to the power sequencing problem - it's not
exposing the individual inputs to the device but rather is a block that
manages everything but needs a bit of a kick to get things going (I'd
guess that with ACPI it'd be triggered via AML).  It's in the same space
but it's not quite the same issue I think, something that can handle
control of the individual resources might still struggle with this.

Well, to me it looks very similar to those resouses we could manage
with the mmc pwrseq, for SDIO. It's also typically the same kind of
combo-chips that moved from supporting SDIO to PCIe, for improved
performance I guess. More importantly, the same constraint to
pre-power on the device is needed to allow it to be discovered/probed.

In our case we'd definitely use pwrseq for PCIe bus and we can also
benefit from using pwrseq for serdev and for platform busses also (for
the same story of WiFi+BT chips).

I can take a look at rewriting pwrseq code to also handle the PCIe
bus. Rewriting it to be a generic lib seems like an easy task,
plugging it into PCIe code would be more fun.

Platform and serdev... Definitely even more fun.

Therefore, I think it would be worth having a common solution for
this, rather than a solution per subsystem or even worse, per device.

Unfortunately, it looks like Peter's email is bouncing so we can't get
an update from him.

Let's see if the kernel.org email will get to him.

-- 
With best wishes
Dmitry