From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: Mingchuang Qiao <mingchuang.qiao@mediatek.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
Bjorn Helgaas <bhelgaas@google.com>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Utkarsh H Patel <utkarsh.h.patel@intel.com>,
linux-pci@vger.kernel.org, matthias.bgg@gmail.com,
lambert.wang@mediatek.com, linux-mediatek@lists.infradead.org,
haijun.liu@mediatek.com, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
Alex Williamson <alex.williamson@redhat.com>
Subject: Re: [PATCH v2] PCI: Re-enable downstream port LTR if it was previously enabled
Date: Fri, 22 Jan 2021 12:05:45 +0200 [thread overview]
Message-ID: <20210122100545.GL1988617@lahna.fi.intel.com> (raw)
In-Reply-To: <1611298991.5980.42.camel@mcddlt001>
Hi,
On Fri, Jan 22, 2021 at 03:03:11PM +0800, Mingchuang Qiao wrote:
> On Thu, 2021-01-21 at 16:31 -0600, Bjorn Helgaas wrote:
> > [+cc Alex and Mingchuang et al from
> > https://lore.kernel.org/r/20210112072739.31624-1-mingchuang.qiao@mediatek.com]
> >
> > On Tue, Jan 19, 2021 at 04:14:10PM +0300, Mika Westerberg wrote:
> > > PCIe r5.0, sec 7.5.3.16 says that the downstream ports must reset the
> > > LTR enable bit if the link goes down (port goes DL_Down status). Now, if
> > > we had LTR previously enabled and the PCIe endpoint gets hot-removed and
> > > then hot-added back the ->ltr_path of the downstream port is still set
> > > but the port now does not have the LTR enable bit set anymore.
> > >
> > > For this reason check if the bridge upstream had LTR enabled previously
> > > and re-enable it before enabling LTR for the endpoint.
> > >
> > > Reported-by: Utkarsh H Patel <utkarsh.h.patel@intel.com>
> > > Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> >
> > I think this and Mingchuang's patch, which is essentially identical,
> > are right and solves the problem for hot-remove/hot-add. In that
> > scenario we call pci_configure_ltr() on the hot-added device, and
> > with this patch, we'll re-enable LTR on the bridge leading to the new
> > device before enabling LTR on the new device itself.
> >
> > But don't we have a similar problem if we simply do a Fundamental
> > Reset on a device? I think the reset path will restore the device's
> > state, including PCI_EXP_DEVCTL2, but it doesn't do anything with the
> > upstream bridge, does it?
> >
>
> Yes. I think the same problem exists under such scenario, and that’s the
> issue my patch intends to resolve.
> I also prepared a v2 patch for review(update the patch description).
> Shall I submit the v2 patch for review?
I looked at your patch and indeed it is essentially doing the same as
this one. So let's forget this patch and go forward with yours :)
Would you like to expand your patch to handle the reset case too that
Bjorn desribes below?
> > So if a bridge and a device below it both have LTR enabled, can't we
> > have the following:
> >
> > - bridge LTR enabled
> > - device LTR enabled
> > - reset device, e.g., via Secondary Bus Reset
> > - link goes down, bridge disables LTR
> > - link comes back up, LTR disabled in both bridge and device
> > - restore device state, including LTR enable
> > - device sends LTR message
> > - bridge reports Unsupported Request
next prev parent reply other threads:[~2021-01-22 10:25 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-19 13:14 [PATCH v2] PCI: Re-enable downstream port LTR if it was previously enabled Mika Westerberg
2021-01-21 22:31 ` Bjorn Helgaas
2021-01-22 7:03 ` Mingchuang Qiao
2021-01-22 10:05 ` Mika Westerberg [this message]
2021-01-22 13:20 ` Bjorn Helgaas
2021-01-25 10:14 ` Mingchuang Qiao
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