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

[Wu Zongyong]

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