linux-kernel - Re: [PATCH v8 7/8] thermal: Add PCIe cooling driver

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Message-ID: <CAJZ5v0g+4ZorOVrC_Pr8BvhDUXckqg5WqREw2Wz+8_WzL_d52g@mail.gmail.com>
Date: Thu, 17 Oct 2024 14:58:19 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>, linux-pci@...r.kernel.org, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Lorenzo Pieralisi <lorenzo.pieralisi@....com>, 
	Rob Herring <robh@...nel.org>, Krzysztof Wilczyński <kw@...ux.com>, 
	"Maciej W. Rozycki" <macro@...am.me.uk>, Lukas Wunner <lukas@...ner.de>, 
	Alexandru Gagniuc <mr.nuke.me@...il.com>, Krishna chaitanya chundru <quic_krichai@...cinc.com>, 
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, linux-pm@...r.kernel.org, 
	Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>, 
	Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>, 
	Lukasz Luba <lukasz.luba@....com>, LKML <linux-kernel@...r.kernel.org>, 
	Amit Kucheria <amitk@...nel.org>, Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: Re: [PATCH v8 7/8] thermal: Add PCIe cooling driver

On Thu, Oct 17, 2024 at 2:16 PM Ilpo Järvinen
<ilpo.jarvinen@...ux.intel.com> wrote:
>
> On Thu, 17 Oct 2024, Jonathan Cameron wrote:
>
> > On Wed,  9 Oct 2024 12:52:22 +0300
> > Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com> wrote:
> >
> > > Add a thermal cooling driver to provide path to access PCIe bandwidth
> > > controller using the usual thermal interfaces.
> > >
> > > A cooling device is instantiated for controllable PCIe Ports from the
> > > bwctrl service driver.
> > >
> > > If registering the cooling device fails, allow bwctrl's probe to
> > > succeed regardless. As cdev in that case contains IS_ERR() pseudo
> > > "pointer", clean that up inside the probe function so the remove side
> > > doesn't need to suddenly make an odd looking IS_ERR() check.
> > >
> > > The thermal side state 0 means no throttling, i.e., maximum supported
> > > PCIe Link Speed.
> > >
> > > Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> > > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> > > Acked-by: Rafael J. Wysocki <rafael@...nel.org> # From the cooling device interface perspective
> >
> > Trivial thing noticed on a reread.
> >
> >
> > > diff --git a/drivers/thermal/Kconfig b/drivers/thermal/Kconfig
> > > index 61e7ae524b1f..d3f9686e26e7 100644
> > > --- a/drivers/thermal/Kconfig
> > > +++ b/drivers/thermal/Kconfig
> > > @@ -220,6 +220,15 @@ config DEVFREQ_THERMAL
> > >
> > >       If you want this support, you should say Y here.
> > >
> > > +config PCIE_THERMAL
> > > +   bool "PCIe cooling support"
> > > +   depends on PCIEPORTBUS
> > > +   help
> > > +     This implements PCIe cooling mechanism through bandwidth reduction
> > > +     for PCIe devices.
> >
> > Technically links not devices, but don't think that matters much
>
> That distinction would be splitting hairs beyond what seems useful from
> ordinary user's point of view. If there's no device attached, BW
> controller cannot do anything since the link is not going to train.
> The link speed reduction is going to impact the speed the device
> can communicate with even if it technically occurs on the link.

>From the Kconfig description perspective I think it's better to say
"devices" even though technically it is about links, because device
performance is what users will measure and notice any changes of.