From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Lukas Wunner <lukas@wunner.de>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andreas Noever <andreas.noever@gmail.com>,
Linux PCI <linux-pci@vger.kernel.org>,
Linux PM <linux-pm@vger.kernel.org>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
Mika Westerberg <mika.westerberg@linux.intel.com>
Subject: Re: [PATCH v5 2/8] PCI: Allow runtime PM on Thunderbolt ports
Date: Mon, 30 Jan 2017 08:15:40 +0100 [thread overview]
Message-ID: <CAJZ5v0gZgp0RVo_2toASw+-GF=FV8=TdEmauP+7+-czU5kshjg@mail.gmail.com> (raw)
In-Reply-To: <20170128220914.GN20550@bhelgaas-glaptop.roam.corp.google.com>
On Sat, Jan 28, 2017 at 11:09 PM, Bjorn Helgaas <helgaas@kernel.org> wrote:
> On Sun, Jan 15, 2017 at 09:03:45PM +0100, Lukas Wunner wrote:
>> Currently PCIe ports are only allowed to go to D3 if the BIOS is dated
>> 2015 or newer to avoid potential issues with old chipsets. However for
>> Thunderbolt we know that even the oldest controller, Light Ridge (2010),
>> is able to suspend its ports to D3 just fine.
>>
>> We're about to add runtime PM for Thunderbolt on the Mac. Apple has
>> released two EFI security updates in 2015 which encompass all machines
>> with Thunderbolt, but the achieved power saving should be made available
>> to users even if they haven't updated their BIOS. To this end,
>> special-case Thunderbolt in pci_bridge_d3_possible().
>
> I think this whole paragraph is unnecessary detail. I first thought
> you had some connection with a firmware security issue, but now I see
> the only point is that if you have pre-2015 firmware, you could update
> it since newer firmware is available.
>
>> This allows the Thunderbolt controller to power down but the root port
>> to which the Thunderbolt controller is attached remains in D0 unless
>> the EFI update is installed. Users can pass pcie_port_pm=force on the
>> kernel command line if they cannot install the EFI update but still want
>> to benefit from the additional power saving of putting the root port
>> into D3. In practice, root ports can be suspended to D3 without issues
>> at least on 2012 Ivy Bridge machines.
>
> I'm not sure I like advertising pcie_port_pm=force. That just means a
> few leet folks will use this parameter and run in a subtly different
> configuration than everybody else, and possibly trip over subtly
> different issues. The audience (users who read kernel change logs and
> are willing to use special boot parameters, but who can't install an
> EFI update) seems small.
That basically is for somebody who has a product and knows that the
feature works there, but doesn't want or simply can't patch the kernel
(which is shipped by a distro or similar).
Thanks,
Rafael
next prev parent reply other threads:[~2017-01-30 7:15 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-15 20:03 [PATCH v5 0/8] Runtime PM for Thunderbolt on Macs Lukas Wunner
2017-01-15 20:03 ` [PATCH v5 8/8] thunderbolt: Runtime suspend NHI when idle Lukas Wunner
2017-01-15 20:03 ` [PATCH v5 6/8] PM / sleep: Define constant for direct_complete Lukas Wunner
2017-01-15 20:03 ` [PATCH v5 3/8] PCI: Don't block runtime PM for Thunderbolt host hotplug ports Lukas Wunner
2017-01-16 10:29 ` Mika Westerberg
2017-01-28 23:00 ` Bjorn Helgaas
2017-02-10 18:39 ` Bjorn Helgaas
2017-02-12 17:13 ` Lukas Wunner
2017-02-13 12:17 ` Rafael J. Wysocki
2017-01-15 20:03 ` [PATCH v5 7/8] thunderbolt: Power down controller when idle Lukas Wunner
2017-01-28 23:32 ` Bjorn Helgaas
2017-02-12 16:31 ` Lukas Wunner
2017-02-13 22:57 ` Bjorn Helgaas
2017-01-15 20:03 ` [PATCH v5 1/8] PCI: Recognize Thunderbolt devices Lukas Wunner
2017-01-28 21:52 ` Bjorn Helgaas
2017-01-29 0:26 ` Lukas Wunner
2017-02-06 6:09 ` Lukas Wunner
2017-02-10 17:42 ` Bjorn Helgaas
2017-02-12 16:50 ` Lukas Wunner
2017-01-15 20:03 ` [PATCH v5 2/8] PCI: Allow runtime PM on Thunderbolt ports Lukas Wunner
2017-01-28 22:09 ` Bjorn Helgaas
2017-01-30 7:15 ` Rafael J. Wysocki [this message]
2017-02-10 17:57 ` Bjorn Helgaas
2017-01-15 20:03 ` [PATCH v5 4/8] Revert "PM / Runtime: Remove the exported function pm_children_suspended()" Lukas Wunner
2017-01-15 20:03 ` [PATCH v5 5/8] PM: Make requirements of dev_pm_domain_set() more precise Lukas Wunner
2017-01-28 23:14 ` Bjorn Helgaas
2017-01-19 10:38 ` [PATCH v5 0/8] Runtime PM for Thunderbolt on Macs Greg Kroah-Hartman
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