linux-kernel - Re: [PATCH 1/1] PCI: dwc: Use regular interrupt instead of chained

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Date:   Thu, 13 Jul 2023 12:03:55 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Radu Rendec <rrendec@...hat.com>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczynski <kw@...ux.com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pali Rohár <pali@...nel.org>
Subject: Re: [PATCH 1/1] PCI: dwc: Use regular interrupt instead of chained

On Thu, Jun 29, 2023 at 11:04:50PM -0400, Radu Rendec wrote:
> On Thu, 2023-06-29 at 17:11 -0500, Bjorn Helgaas wrote:
> ...

> > If converting from chained to normal handlers can be done safely, I
> > would definitely be in favor if doing it across all of drivers/pci/ at
> > once so they're all consistent.  Otherwise that code just gets copied
> > to new drivers, so the issue persists and spreads.
> 
> I think the conversion can be done safely, meaning that it won't break
> the drivers. And by the way, there are other IRQ drivers (outside the
> PCI space) that use chained interrupts.
> 
> Unfortunately, it seems we are going in circles. Chained interrupts are
> bad because they let IRQ storms go unnoticed and lock up the system,
> but converting them to regular interrupts is also bad because it breaks
> the userspace ABI.
> 
> I am willing to help clean up this mess, but I think first we need to
> come up with a solution that's acceptable for everybody. I was hoping
> Marc and Thomas would chime in, but unfortunately that hasn't happened
> yet - other than each of them pointing out (separately) what is wrong
> with each approach.

I don't think Marc or Thomas are going to chime in with a fully-formed
solution.  I think to make progress, you (or Pali, or somebody) will
have to try to address Marc and Thomas' comments, make a proposal, and
we can iterate on it.

Bjorn