linux-kernel - Re: Is it possible to change IRQ for certain device?

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Message-ID: <3e8340490801132130l737e166i3f957518170b98fc@mail.gmail.com>
Date:	Mon, 14 Jan 2008 00:30:48 -0500
From:	"Bryan Donlan" <bdonlan@...il.com>
To:	"Lee Revell" <rlrevell@...-job.com>
Cc:	"Jan Marek" <linux@...ard.jcu.cz>,
	"linux-os (Dick Johnson)" <linux-os@...logic.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: Is it possible to change IRQ for certain device?

On Jan 13, 2008 10:57 PM, Lee Revell <rlrevell@...-job.com> wrote:
> On Jan 11, 2008 11:57 AM, Jan Marek <linux@...ard.jcu.cz> wrote:
> > I suppose, that VGA card does not need unique IRQ, but programmers,
> > which wrote driver, want it. I can imagine, that VGA card have many
> > interrupts, especially in the OpenGL games, but I cannot assign unique
> > IRQ for VGA card at all :-(
> >
> > But thank you for advice: I will try to send e-mail to Gigabyte and ask
> > they, if it possible to do change in the BIOS.
> >
> > BTW: it is interesting: I had a Biostar TA690G motherboard and it behave
> > similar as Gigabyte: I cannnot assign unique IRQ to the external
> > graphics card... Chipsets of this motherboards are the same...
> >
> > I've tried to solve this problem by bought of new motherboard: Gigabyte
> > MA790FX-DS5. I will see, if this board will behave as previous board...
>
> Why is a shared IRQ a problem for you?  IRQ handlers are supposed to
> be fast enough that disabling an IRQ line for the duration of the
> handler execution should not be a problem even if the IRQ is shared.
> VGA interrupts in particular should only fire once per frame and only
> need to flip some bits to wake up any processes waiting on vsync.
>
> If you have issues with a shared VGA interrupt then the bug is that
> some IRQ handler runs for too long and should be deferring work to a
> bottom half.

Jan is apparently using the nvidia binary driver, so I doubt it will
be possible to fix the bug that prevents it from sharing IRQs.
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