Re: Why MSI is limited to 32 interrupts maximum

[okaya]

On 2016-10-15 06:30, Bharat Kumar Gogada wrote:

On Sat, 15 Oct 2016 12:37:55 +
Bharat Kumar Gogada  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.

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Re: Why MSI is limited to 32 interrupts maximum

[okaya]

On 2016-10-15 06:30, Bharat Kumar Gogada wrote:

On Sat, 15 Oct 2016 12:37:55 +
Bharat Kumar Gogada  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 majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

RE: Why MSI is limited to 32 interrupts maximum

[Bharat Kumar Gogada]

 > On Sat, 15 Oct 2016 12:37:55 +
> Bharat Kumar Gogada  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 ?

> >
> > 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.

RE: Why MSI is limited to 32 interrupts maximum

[Bharat Kumar Gogada]

 > On Sat, 15 Oct 2016 12:37:55 +
> Bharat Kumar Gogada  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 ?

> >
> > 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.

Re: Why MSI is limited to 32 interrupts maximum

[Marc Zyngier]

On Sat, 15 Oct 2016 12:37:55 +
Bharat Kumar Gogada  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
> 
> 
> 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.

Re: Why MSI is limited to 32 interrupts maximum

[Marc Zyngier]

On Sat, 15 Oct 2016 12:37:55 +
Bharat Kumar Gogada  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
> 
> 
> 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.