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
>> > named recipient(s) and contain(s) confidential information that may be
>> > proprietary, privileged or copyrighted under applicable law. If you
>> > are not the intended recipient, do not read, copy, or forward this
>> > email message or any attachments. Delete this email message and any
>> > attachments immediately.
>> >
>>
>> Please fix your email not to carry such disclaimer (or use a private
>> email address
>> if you can't work around your company policy). Posting confidential
>> information
>> on a public mailing list feels a bit silly.
>>
>> Thanks,
>>
>> M.
>> --
>> Without deviation from the norm, progress is not possible.
> --
> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
prev parent reply other threads:[~2016-10-15 16:39 UTC|newest]
Thread overview: 4+ 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 13:14 ` Marc Zyngier
2016-10-15 13:30 ` Bharat Kumar Gogada
2016-10-15 16:39 ` okaya [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=304288d1efe5014b24d600be4438651a@codeaurora.org \
--to=okaya@codeaurora.org \
--cc=arnd@arndb.de \
--cc=bharat.kumar.gogada@xilinx.com \
--cc=helgaas@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pci-owner@vger.kernel.org \
--cc=linux-pci@vger.kernel.org \
--cc=marc.zyngier@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).