linux-kernel - Re: [RFC PATCH] PCI: avoid SBR for NVIDIA T4

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Date:   Fri, 31 Mar 2023 10:11:15 +0800
From:   Wu Zongyong <wuzongyong@...ux.alibaba.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     sdonthineni@...dia.com, bhelgaas@...gle.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        wllenyj@...ux.alibaba.com, wutu.xq2@...ux.alibaba.com,
        gerry@...ux.alibaba.com
Subject: Re: [RFC PATCH] PCI: avoid SBR for NVIDIA T4

On Thu, Mar 30, 2023 at 10:49:26AM -0500, Bjorn Helgaas wrote:
> On Thu, Mar 30, 2023 at 10:10:16AM +0800, Wu Zongyong wrote:
> > On Wed, Mar 29, 2023 at 12:05:15PM -0500, Bjorn Helgaas wrote:
> > > On Wed, Mar 29, 2023 at 07:58:45PM +0800, Wu Zongyong wrote:
> > > > Secondary bus reset will fail if NVIDIA T4 card is direct attached to a
> > > > root port.
> > > 
> > > Is this only a problem when direct attached to a Root Port?  Why would
> > > that be?  If it's *not* related to being directly under a Root Port,
> > > don't mention that at all.
> >
> > Yes, this problem occurs only when the T4 card is direct attached to a
> > Root Port.
> > I have test it with a T4 card attached to a PCIe Switch or a PCI Bridge,
> > and it works well.
> 
> From an electrical and protocol point of view, the device should not
> be able to tell the difference, so Lukas' suggestion that it may be
> related to reset delays seems very pertinent.
I will test it with the commits mentioned above.
But it may take some time since it is not easy to replace kernel in our
environment.
> 
> Bjorn