linux-kernel - Re: [PATCH] PCI/ASPM: Should not report ASPM support to BIOS if FADT indicates ASPM is unsupported

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Message-ID: <20220715224911.GA1208192@bhelgaas>
Date:   Fri, 15 Jul 2022 17:49:11 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Manyi Li <limanyi@...ontech.com>
Cc:     Matthew Garrett <mjg59@...f.ucam.org>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        bhelgaas@...gle.com, refactormyself@...il.com, kw@...ux.com,
        rajatja@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Vidya Sagar <vidyas@...dia.com>,
        rafael@...nel.org
Subject: Re: [PATCH] PCI/ASPM: Should not report ASPM support to BIOS if FADT
 indicates ASPM is unsupported

Manyi, FYI, your emails aren't making it to the linux-pci list (or to
me), so I'm missing most of this conversation.

If you look at the lore archive:
  https://lore.kernel.org/all/20220713112612.6935-1-limanyi@uniontech.com/
you'll see all the message-ids that are not found.

Maybe you're sending HTML or something else vger doesn't like?
http://vger.kernel.org/majordomo-info.html#taboo

On Fri, Jul 15, 2022 at 10:32:36AM +0100, Matthew Garrett wrote:
> On Fri, Jul 15, 2022 at 05:19:25PM +0800, Manyi Li wrote:
> > On 2022/7/15 16:29, Matthew Garrett wrote:
> > > On Fri, Jul 15, 2022 at 03:40:36PM +0800, Manyi Li wrote:
> > > 
> > > > Please see the details of this issus:
> > > > https://bugzilla.kernel.org/show_bug.cgi?id=216245
> > > 
> > > Hmm. The only case where changing aspm_support_enabled to false should
> > > matter is in pcie_aspm_init_link_state(), where it looks like we'll
> > > potentially rewrite some registers even if aspm_disabled is true. I
> > > think in theory we shouldn't actually modify anything as a result, and
> > > the lspcis from the bug don't show any ASPM values having changed, but I
> > > don't trust Realtek hardware in the general case so maybe it gets upset
> > > here? If the proposed patch is to just set aspm_support_enabled to false
> > > when we see the FADT bit set then I think this is fine.
> > > 
> > 
> > "aspm_support_enabled" alse be used in calculate_support():
> > if (pcie_aspm_support_enabled())
> >     support |= OSC_PCI_ASPM_SUPPORT | OSC_PCI_CLOCK_PM_SUPPORT;
> > When set OSC_PCI_ASPM_SUPPORT | OSC_PCI_CLOCK_PM_SUPPORT, cause this AER
> > issue. I want don't set OSC_PCI_ASPM_SUPPORT | OSC_PCI_CLOCK_PM_SUPPORT when
> > we see the FADT bit set.
> 
> Oh hm. Are you sure it's the OSC call that breaks it? I have some 
> recollection that I verified the behaviour of Windows here, but it's 
> been over 10 years since I touched this so I could well be wrong. I can 
> try to set up a test env to verify the behaviour of Windows when it 
> comes to _OSC if the FADT says ASPM is unsupported.