From: Bjorn Helgaas <helgaas@kernel.org>
To: Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc: "Johan Hovold" <johan+linaro@kernel.org>,
"Lorenzo Pieralisi" <lpieralisi@kernel.org>,
"Krzysztof Wilczyński" <kw@linux.com>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Andy Gross" <agross@kernel.org>,
"Bjorn Andersson" <andersson@kernel.org>,
"Konrad Dybcio" <konrad.dybcio@linaro.org>,
"Manivannan Sadhasivam" <mani@kernel.org>,
"Rob Herring" <robh@kernel.org>,
"Nirmal Patel" <nirmal.patel@linux.intel.com>,
"Jonathan Derrick" <jonathan.derrick@linux.dev>,
linux-arm-msm@vger.kernel.org, linux-pci@vger.kernel.org,
linux-kernel@vger.kernel.org, stable@vger.kernel.org,
"Michael Bottini" <michael.a.bottini@linux.intel.com>,
"David E . Box" <david.e.box@linux.intel.com>,
"Manivannan Sadhasivam" <manivannan.sadhasivam@linaro.org>
Subject: Re: [PATCH v2 1/6] PCI/ASPM: Add locked helper for enabling link state
Date: Tue, 12 Dec 2023 15:27:07 -0600 [thread overview]
Message-ID: <20231212212707.GA1021099@bhelgaas> (raw)
In-Reply-To: <CAAd53p59q3D7u01ECsgRUgkDkTkchV-Gv+q=TMFcC44_tOs51Q@mail.gmail.com>
On Tue, Dec 12, 2023 at 11:48:27AM +0800, Kai-Heng Feng wrote:
> On Fri, Dec 8, 2023 at 4:47 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> ...
> > I hope we can obsolete this whole idea someday. Using pci_walk_bus()
> > in qcom and vmd to enable ASPM is an ugly hack to work around this
> > weird idea that "the OS isn't allowed to enable more ASPM states than
> > the BIOS did because the BIOS might have left ASPM disabled because it
> > knows about hardware issues." More history at
> > https://lore.kernel.org/linux-pci/20230615070421.1704133-1-kai.heng.feng@canonical.com/T/#u
> >
> > I think we need to get to a point where Linux enables all supported
> > ASPM features by default. If we really think x86 BIOS assumes an
> > implicit contract that the OS will never enable ASPM more
> > aggressively, we might need some kind of arch quirk for that.
>
> The reality is that PC ODM toggles ASPM to workaround hardware
> defects, assuming that OS will honor what's set by the BIOS.
> If ASPM gets enabled for all devices, many devices will break.
That's why I mentioned some kind of arch quirk. Maybe we're forced to
do that for x86, for instance. But even that is a stop-gap.
The idea that the BIOS ASPM config is some kind of handoff protocol is
really unsupportable.
Do we have concrete examples of where enabling ASPM for a device that
advertises ASPM support will break something?
Bjorn
next prev parent reply other threads:[~2023-12-12 21:27 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20231128081512.19387-1-johan+linaro@kernel.org>
2023-11-28 8:15 ` [PATCH v2 1/6] PCI/ASPM: Add locked helper for enabling link state Johan Hovold
2023-12-07 20:47 ` Bjorn Helgaas
2023-12-08 8:00 ` Johan Hovold
2023-12-08 17:39 ` Bjorn Helgaas
2023-12-12 9:25 ` Ilpo Järvinen
2023-12-12 3:48 ` Kai-Heng Feng
2023-12-12 21:27 ` Bjorn Helgaas [this message]
2023-12-13 19:48 ` David E. Box
2023-12-13 20:45 ` Bjorn Helgaas
2023-12-13 23:39 ` David E. Box
2023-12-14 17:28 ` Bjorn Helgaas
2023-11-28 8:15 ` [PATCH v2 2/6] PCI: vmd: Fix deadlock when enabling ASPM Johan Hovold
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