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

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Date:   Thu, 22 Jun 2023 11:33:30 -0500
From:   Terry Bowman <Terry.Bowman@....com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.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

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.

Regards,
Terry