linux-kernel - Re: Why MSI is limited to 32 interrupts maximum

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Message-ID: <20161015141401.70d95035@why.wild-wind.fr.eu.org>
Date:   Sat, 15 Oct 2016 14:14:01 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
Cc:     "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        "arnd@...db.de" <arnd@...db.de>
Subject: Re: Why MSI is limited to 32 interrupts maximum

On Sat, 15 Oct 2016 12:37:55 +0000
Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com> wrote:

Hi Bharat,

> Can anyone tell why MSI interrupts are limited to maximum 32
> interrupts, even though we have 16bit message data register ?

That's the very definition of the original PCI MSI: Up to 32
consecutive interrupts per function, and a single doorbell address.
MSI-X lifts that restriction and offers up to 2048 interrupts that do
not have to be contiguous can target individual doorbells. Assuming
your MSI controller advertises MSI-X support and that your devices do
support it as well, you'll be able to enjoy those.

> 
> Regards,
> Bharat
> 
> 
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	M.
-- 
Without deviation from the norm, progress is not possible.