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

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Message-ID: <70507175-dc7d-d334-4a2a-988239f380a6@linux.intel.com>
Date: Thu, 17 Oct 2024 15:16:05 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
cc: 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, 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.

-- 
 i.