linux-kernel - Re: [PATCH 1/2] PCI: qcom: Switch to bus notifier for enabling ASPM of PCI devices

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Message-ID: <aHZKCXNu6k0hZbVg@hovoldconsulting.com>
Date: Tue, 15 Jul 2025 14:31:05 +0200
From: Johan Hovold <johan@...nel.org>
To: Manivannan Sadhasivam <mani@...nel.org>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH 1/2] PCI: qcom: Switch to bus notifier for enabling ASPM
 of PCI devices

On Tue, Jul 15, 2025 at 03:57:12PM +0530, Manivannan Sadhasivam wrote:
> On Tue, Jul 15, 2025 at 11:33:16AM GMT, Johan Hovold wrote:
> > On Tue, Jul 15, 2025 at 02:41:23PM +0530, Manivannan Sadhasivam wrote:
> > > On Tue, Jul 15, 2025 at 09:48:30AM GMT, Johan Hovold wrote:

> > > > A problem with this approach is that ASPM will never be enabled (and
> > > > power consumption will be higher) in case an endpoint driver is missing.
> > > 
> > > I'm aware of this limiation. But I don't think we should really worry about that
> > > scenario. No one is going to run an OS intentionally with a PCI device and
> > > without the relevant driver. If that happens, it might be due to some issue in
> > > driver loading or the user is doing it intentionally. Such scenarios are short
> > > lived IMO.
> > 
> > There may not even be a driver (yet). A user could plug in whatever
> > device in a free slot. I can also imagine someone wanting to blacklist
> > a driver temporarily for whatever reason.
> 
> Yes, that's why I said these scenarios are 'shortlived'.

My point is the opposite; that you should not make such assumptions
(e.g. hardware not supported by linux or drivers disabled due to
stability or security concerns).

Johan