linux-kernel - Re: [PATCH 04/24] thunderbolt: Add MSI-X support

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Message-ID: <20170522110116.GV8541@lahna.fi.intel.com>
Date:   Mon, 22 May 2017 14:01:16 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     "Bernat, Yehezkel" <yehezkel.bernat@...el.com>
Cc:     Andreas Noever <andreas.noever@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Jamet, Michael" <michael.jamet@...el.com>,
        Lukas Wunner <lukas@...ner.de>,
        "Levy, Amir (Jer)" <amir.jer.levy@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Mario.Limonciello@...l.com" <Mario.Limonciello@...l.com>,
        "Jared.Dominguez@...l.com" <Jared.Dominguez@...l.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/24] thunderbolt: Add MSI-X support

On Mon, May 22, 2017 at 10:35:08AM +0000, Bernat, Yehezkel wrote:
> 
> 
> > -----Original Message-----
> > From: Mika Westerberg [mailto:mika.westerberg@...ux.intel.com]
> > Sent: Monday, May 22, 2017 11:52
> > To: Andreas Noever <andreas.noever@...il.com>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>; Jamet, Michael
> > <michael.jamet@...el.com>; Bernat, Yehezkel
> > <yehezkel.bernat@...el.com>; Lukas Wunner <lukas@...ner.de>; Levy,
> > Amir (Jer) <amir.jer.levy@...el.com>; Andy Lutomirski <luto@...nel.org>;
> > Mario.Limonciello@...l.com; Jared.Dominguez@...l.com; Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com>; linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH 04/24] thunderbolt: Add MSI-X support
> > 
> > On Sun, May 21, 2017 at 07:51:09PM +0200, Andreas Noever wrote:
> > > On Thu, May 18, 2017 at 4:38 PM, Mika Westerberg
> > > <mika.westerberg@...ux.intel.com> wrote:
> > > > Intel Thunderbolt controllers support up to 16 MSI-X vectors. Using
> > > Is that true for all generations? If so can we remove the legacy path?
> > 
> > Yes, I think it has been the case from the beginning. I have here one
> > Mac Mini with Light Ridge and even it has working MSI-X.
> > 
> > Yehezkel, Michael, Amir, do you know if that's the case for all other
> > controller as well?
> 
> We are checking it, but what if we don't get the MSI-X we need?
> Don't we have to support MSI as a fallback option or maybe we are sure
> this will never happen in modern kernels?

Indeed, I think it makes sense to keep the fallback code just to be sure
it still works if for some reason we don't get the MSI-X vectors. I
think there is even a command line option to turn MSI-(X) off
completely.

Regarding this, I see that I'm missing a flag in the second call:

  pci_alloc_irq_vectors(pdev, 1, 1, PCI_IRQ_MSI);

should probably be 

  pci_alloc_irq_vectors(pdev, 1, 1, PCI_IRQ_MSI | PCI_IRQ_LEGACY);

instead to make it work with legacy IRQs as well.