From: okaya@codeaurora.org
To: Bharat Kumar Gogada <bharat.kumar.gogada@xilinx.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>,
linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
Bjorn Helgaas <helgaas@kernel.org>,
arnd@arndb.de, linux-pci-owner@vger.kernel.org
Subject: Re: Why MSI is limited to 32 interrupts maximum
Date: Sat, 15 Oct 2016 09:39:24 -0700 [thread overview]
Message-ID: <304288d1efe5014b24d600be4438651a@codeaurora.org> (raw)
In-Reply-To: <8520D5D51A55D047800579B0941471982594B127@XAP-PVEXMBX01.xlnx.xilinx.com>
On 2016-10-15 06:30, Bharat Kumar Gogada wrote:
>> On Sat, 15 Oct 2016 12:37:55 +0000
>> Bharat Kumar Gogada <bharat.kumar.gogada@xilinx.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.
>>
>
> Thanks Marc, so then only 5 bits of message data register will be
> used, so what is the purpose rest of the bits ?
>
Data field is used to indicate which interrupt number is used. It does
not need to start at 0.
You have 32 consecutive interrupts starting from some arbitrary base.
>> >
>> > Regards,
>> > Bharat
>> >
>> >
>> > This email and any attachments are intended for the sole use of the
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>> Please fix your email not to carry such disclaimer (or use a private
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>>
>> Thanks,
>>
>> M.
>> --
>> Without deviation from the norm, progress is not possible.
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prev parent reply other threads:[~2016-10-15 16:39 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-15 12:37 Why MSI is limited to 32 interrupts maximum Bharat Kumar Gogada
2016-10-15 12:37 ` Bharat Kumar Gogada
2016-10-15 13:14 ` Marc Zyngier
2016-10-15 13:30 ` Bharat Kumar Gogada
2016-10-15 13:30 ` Bharat Kumar Gogada
2016-10-15 16:39 ` okaya [this message]
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