Re: Dump of registers during endpoint link down

[Bjorn Helgaas <helgaas@kernel.org>]

Reply-all and don't top-post.  See
https://people.kernel.org/tglx/notes-about-netiquette

On Mon, Jul 13, 2020 at 03:31:02PM +0530, Manish Raturi wrote:
> Thanks, Bjorn, I am doing that (lspci -vvvxxxx) to dump all the
> register, but in case of Link down, are there any specific registers
> which we should look in, mostly I look below register:
> 
> 1) Link status /control/capability
> 2) Slot status /control/capability
> 3) Lane error status registers.
> 
> Any other register we can specifically look for.

I have no idea what the problem is, so can't really help you, sorry.
All you've said is that the link to an endpoint is down.  I don't know
whether the the slot is even powered up.  You could try a different
card to see whether that works.  You could try the same card in a
different machine to see if that works.  If you think the link
*should* be up, you could always debug it from a hardware point of
view with a PCIe analyzer.

> On Fri, Jul 10, 2020 at 12:54 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
> > On Thu, Jul 09, 2020 at 12:44:24PM +0530, Manish Raturi wrote:
> > > Hi Team,
> > >
> > > I have a generic query , if an hotplug pcie endpoint connected to the
> > > CPU root port shows link down, then from the debugging perspective
> > > w.r.t PCIE what all register can be dump during the failure condition,
> > > what I can think of is these registers from the root port side
> > >
> > > 1) Link status /control/capability
> > > 2) Slot status /control/capability
> > > 3) Lane error status registers.
> > >
> > > Anything else we can dump which gives us more insight into the issue.
> > > Also is there anything by which we can check from PCIE clock
> > > perspective.
> >
> > If you have this:
> >
> >   Root Port ----- Endpoint
> >
> > and the Link is down, you won't be able to read any registers from the
> > Endpoint.  You can dump all the Root Port registers, of course, e.g.,
> > with "lspci -vvvxxxx".