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Message-ID: <1dcc3ca74c3fbb3b4a1adcafb648dfd2501310f1.camel@kernel.org>
Subject: Re: [PATCH] PCI/portdrv: Disable bwctrl service if port is fixed at
 2.5 GT/s
From: Niklas Schnelle <niks@kernel.org>
To: Lukas Wunner <lukas@wunner.de>, Niklas Schnelle <schnelle@linux.ibm.com>
Cc: Ilpo =?ISO-8859-1?Q?J=E4rvinen?= <ilpo.jarvinen@linux.intel.com>,  Bjorn
 Helgaas <bhelgaas@google.com>, linux-pci@vger.kernel.org, Rob Herring
 <robh@kernel.org>, Krzysztof Wilczy??ski	 <kw@linux.com>, "Maciej W .
 Rozycki" <macro@orcam.me.uk>, Jonathan Cameron	
 <Jonathan.Cameron@huawei.com>, Alexandru Gagniuc <mr.nuke.me@gmail.com>, 
 Krishna chaitanya chundru	 <quic_krichai@quicinc.com>, Srinivas Pandruvada	
 <srinivas.pandruvada@linux.intel.com>, "Rafael J . Wysocki"
 <rafael@kernel.org>, 	linux-pm@vger.kernel.org, Smita Koralahalli	
 <Smita.KoralahalliChannabasappa@amd.com>, LKML
 <linux-kernel@vger.kernel.org>,  Daniel Lezcano
 <daniel.lezcano@linaro.org>, Amit Kucheria <amitk@kernel.org>, Zhang Rui
 <rui.zhang@intel.com>,  Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
 Lorenzo Pieralisi <lpieralisi@kernel.org>, Mika Westerberg	
 <mika.westerberg@linux.intel.com>
Date: Thu, 12 Dec 2024 21:40:04 +0100
In-Reply-To: <Z1rX1BgdsPHIHOv4@wunner.de>
References: <20241207-fix_bwctrl_thunderbolt-v1-1-b711f572a705@kernel.org>
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On Thu, 2024-12-12 at 13:32 +0100, Lukas Wunner wrote:
> On Thu, Dec 12, 2024 at 10:17:21AM +0100, Niklas Schnelle wrote:
> > On Thu, 2024-12-12 at 10:08 +0100, Lukas Wunner wrote:
> > > After re-reading the spec I'm convinced now
> > > that we're doing this wrong and that we should honor the Max Link Spe=
ed
> > > instead of blindly deeming all set bits in the Link Capabilities 2
> > > Register as supported speeds:
> > >=20
> > > https://lore.kernel.org/r/e3386d62a766be6d0ef7138a001dabfe563cdff8.17=
33991971.git.lukas@wunner.de/
> > >=20
> > > @Niklas, could you test if this is sufficient to avoid the issue?
> > > Or do we still need to stop instantiating the bandwidth controller
> > > if more than one speed is supported?
> >=20
> > Yes, I will test this but will only get to do so tonight (UTC +2).
>=20
> Hey, no worries.  We're not on the run!
>=20
> > If it's not sufficient I think we could use the modified
> > pcie_get_supported_speeds() to check if only one link speed is
> > supported, right?
>=20
> pcie_get_supported_speeds() is used to fill in the supported_speeds
> field in struct pci_dev.
>=20
> And that field is used in a number of places (exposure of the max link
> speed in sysfs, delay handling in pci_bridge_wait_for_secondary_bus(),
> link tuning in radeon/amdgpu drivers, etc).

Side question. If this is used in radeon/amdgpu could detecting the
thunderbolt port's max link speed as 2.5 GT/s cause issues for external
GPUs?