linux-kernel - Re: [PATCH v6 25/27] cxl/pci: Disable root port interrupts in RCH mode

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Date:   Fri, 23 Jun 2023 14:28:56 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Terry Bowman <Terry.Bowman@....com>
CC:     <alison.schofield@...el.com>, <vishal.l.verma@...el.com>,
        <ira.weiny@...el.com>, <bwidawsk@...nel.org>,
        <dan.j.williams@...el.com>, <dave.jiang@...el.com>,
        <linux-cxl@...r.kernel.org>, <rrichter@....com>,
        <linux-kernel@...r.kernel.org>, <bhelgaas@...gle.com>
Subject: Re: [PATCH v6 25/27] cxl/pci: Disable root port interrupts in RCH
 mode

On Thu, 22 Jun 2023 11:33:30 -0500
Terry Bowman <Terry.Bowman@....com> wrote:

> Hi Jonathan,
> 
> On 6/22/23 08:12, Jonathan Cameron wrote:
> > On Wed, 21 Jun 2023 22:51:24 -0500
> > Terry Bowman <terry.bowman@....com> wrote:
> >   
> >> The RCH root port contains root command AER registers that should not be
> >> enabled.[1] Disable these to prevent root port interrupts.  
> > 
> > I'm a little dubious about a 'because the spec says' so argument.
> > If we can describe the path by which spurious interrupts turn up then
> > great - if not then fair enough.
> >   
> 
> This was added to follow the spec. The RCH downstream port contains
> root port control pci express capability for enabling and disabling root
> port interrupts. The interrupts are (should be) disabled by default at
> powerup according to the PCI spec. We know SW does not enable because
> the RCH downstream port is not enumerated or managed by a port driver. I
> cant say this patch is absolutely necessary but was not comfortable with
> removing it either and want to avoid undefined behavior.
> 
Maybe we should just abuse firmware authors and blame them for potentially
having changed the default :)

Fine as is.

Jonathan

> Regards,
> Terry