linux-kernel - Re: MSI messages

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Message-ID: <4944EAC3.1020407@gmail.com>
Date:	Sun, 14 Dec 2008 15:15:15 +0400
From:	Manu Abraham <abraham.manu@...il.com>
To:	Grant Grundler <grundler@...isc-linux.org>
CC:	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: MSI messages

Grant Grundler wrote:
> On Sat, Dec 13, 2008 at 01:38:24PM +0400, Manu Abraham wrote:
>> Hi,
>>
>> I am wondering how to handle this:
>>
>> Does the kernel somehow handle MSI message readback from the PCI config space 
>> for the MSI message as described in 6.8.1 of the PCI Bus specification 2.3 or 
>> does a device specific driver have to read the Message Address and Data ?
>>
>> To put it short: i am wondering how i should read the MSI messages.
> 
> The "message" is actually mapped to an the interrupt vector by the core
> generic interrupt handling code in the kernel.
> 
> 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 ?

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

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 ?

Regards,
Manu
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