linux-kernel - Re: [PATCH v4 1/9] dt-bindings: imx6q-pcie: Add ref clock for i.MX95 PCIe RC

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Message-ID: <ZxZyjLnSunE60Qo1@lizhi-Precision-Tower-5810>
Date: Mon, 21 Oct 2024 11:26:04 -0400
From: Frank Li <Frank.li@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Richard Zhu <hongxing.zhu@....com>, kw@...ux.com,
	manivannan.sadhasivam@...aro.org, bhelgaas@...gle.com,
	lpieralisi@...nel.org, l.stach@...gutronix.de, robh+dt@...nel.org,
	conor+dt@...nel.org, shawnguo@...nel.org,
	krzysztof.kozlowski+dt@...aro.org, festevam@...il.com,
	s.hauer@...gutronix.de, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, kernel@...gutronix.de,
	imx@...ts.linux.dev
Subject: Re: [PATCH v4 1/9] dt-bindings: imx6q-pcie: Add ref clock for i.MX95
 PCIe RC

On Fri, Oct 18, 2024 at 06:13:05PM -0500, Bjorn Helgaas wrote:
> On Tue, Oct 15, 2024 at 04:33:25PM +0800, Richard Zhu wrote:
> > Previous reference clock of i.MX95 PCIe RC is on when system boot to
> > kernel. But boot firmware change the behavor, it is off when boot. So it
> > needs be turn on when it is used. Also it needs be turn off/on when suspend
> > and resume.
>
> I think this background would make more sense in patch 2.  IIUC,
> that's where the driver behavior changes to do something with the
> "ref" clock.

Yes, use "ref" clock are more reasonable because we have not consider
external osc clock case at beggining.

>
> I'm not sure how to interpret "Previous reference clock of i.MX95 PCIe
> RC is on when system boot to kernel. But boot firmware change the
> behavor, it is off when boot."
>
> Does that mean a previous version of the boot firmware left the ref
> clock on at handoff to the OS, and newer firmware turns it off?  If
> so, I think it would be useful to include information about the
> relevant firmware versions.

i.MX95 is quite new. previous version should be 'preview' boot firmware.
The production version turn ref clock off. Can we simple said "preview"
version. Most people should use production version, which is general
avaible for public.

Frank
>
> > Add one ref clock for i.MX95 PCIe RC. Increase clocks' maxItems to 5 and keep
> > the same restriction with other compatible string.