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

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Message-ID: <20241017142808.00002753@Huawei.com>
Date: Thu, 17 Oct 2024 14:28:08 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
CC: "Rafael J. Wysocki" <rafael@...nel.org>, <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>,
	<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, 17 Oct 2024 16:02:34 +0300 (EEST)
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com> wrote:

> On Thu, 17 Oct 2024, Rafael J. Wysocki wrote:
> 
> > 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.  
> 
> Yes, that's what I tried to explain above. I intend to keep it as 
> "devices" for this very reason.
> 
Fine by me to keep it as things stand. Been reading too many specs
recently so my immediate thought was why is there a bandwidth control
for the engines / memory in the EP :)

Jonathan