linux-kernel - Re: MSI messages

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Date:	Sun, 14 Dec 2008 11:52:39 -0700
From:	Grant Grundler <grundler@...isc-linux.org>
To:	Manu Abraham <abraham.manu@...il.com>
Cc:	Grant Grundler <grundler@...isc-linux.org>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: MSI messages

On Sun, Dec 14, 2008 at 03:15:15PM +0400, Manu Abraham wrote:
...
> > A "GSI" (Generic Sys Interrupt?) is associated with each entry in
> > the MSI-X table. Driver then calls request_irq() to bind an interrupt
> > handler to each GSI. So the driver never directly sees the "message".
> 
> Oh, you mean the array of irq_handlers in the MSI-X table should 
> correspond to a particular message ?

No. I mean each MSI-X entry has an address+message pair and each MSI-X entry
is associated with the parameters passed to each call of request_irq().
Pass in unique private data to each call of request_irq() and the driver
can determine which message was delivered when the ISR gets called.
(ISR == Interrupt Service Routine, aka driver IRQ handler)

> I remember sometime back somebody stated that one might not get 
> the requested number of handlers what you requested. 

Correct. The limit is defined by the number of GSI's available
from the HW.

> In such a case, if the irq_handlers are mapped in a static fashion, one 
> might not get any interrupt callbacks for a specific functionality of 
> the hardware. Or is there something missing in what i understood ?

Correct.

grant
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