linux-kernel - Re: [PATCH v3 2/2] PCI: qcom: properly implement RC shutdown/power up

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Date: Wed, 27 Mar 2024 16:20:50 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Konrad Dybcio <konrad.dybcio@...aro.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Johan Hovold <johan+linaro@...nel.org>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	Bjorn Andersson <quic_bjorande@...cinc.com>
Subject: Re: [PATCH v3 2/2] PCI: qcom: properly implement RC shutdown/power up

On Wed, Mar 27, 2024 at 08:49:09PM +0100, Konrad Dybcio wrote:
> Currently, we've only been minimizing the power draw while keeping the
> RC up at all times. This is suboptimal, as it draws a whole lot of power
> and prevents the SoC from power collapsing.
> 
> Implement full shutdown and re-initialization to allow for powering off
> the controller.
> 
> This is mainly intended for SC8280XP with a broken power rail setup,
> which requires a full RC shutdown/reinit in order to reach SoC-wide
> power collapse, but sleeping is generally better than not sleeping and
> less destructive suspend can be implemented later for platforms that
> support it.

Second try (first at
https://lore.kernel.org/all/20240212213216.GA1145794@bhelgaas/):

  - Capitalize subject lines to match history (sorry, I didn't mention
    the first time)

  - Drop or replace "properly" with something specific

  - "... minimizing power draw while keeping RC up at all times ...
    draws a whole lot of power" doesn't quite make sense to me

  - Reword or explain "power collapse"

  - No COMPILE_TEST provision (maybe it turned out to be impractical?)

  - Magic delay numbers below with no citation or explanation.  Even a
    short comment could be a hint about how to verify and potentially
    change in the future.  A #define for readl_poll_timeout() would be
    helpful as a place for a comment and because the name could
    include "_US" to show the units.

  - Add "()" after function names in comments

Bjorn