linux-kernel - Re: [PATCH v2 -rt] ide: workaround buggy hardware issues with preemptable hardirqs

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Message-ID: <20080628101431.0b64d6c2@lxorguk.ukuu.org.uk>
Date:	Sat, 28 Jun 2008 10:14:31 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	avorontsov@...mvista.com
Cc:	Ingo Molnar <mingo@...e.hu>, linux-ide@...r.kernel.org,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Daniel Walker <dwalker@...sta.com>
Subject: Re: [PATCH v2 -rt] ide: workaround buggy hardware issues with
 preemptable hardirqs

> But some hardware (namely ULi M5228 in the ULi M1575 "Super South Brige")
> behaves in a strange way: it asserts interrupts as edge sensitive. And
> because preemptable IRQ handler disables PIC's interrupt, PIC will likely
> miss it.

You mean "I've programmed the hardware wrong"

If your M5228 is in native mode it should be generating a level trigger,
providing you've programmed it in full that way. If you have it in legacy
mode then it honours IDEIRT and you want the relevant PIC/APIC input set
to level.

How to program an IDE controller out of legacy mode is a public open
standard document.

> It would be great to re-configure the ULi bridge or ULi IDE controller
> to behave sanely, but no one knows how or if this is possible at all
> (no available specifications).

You need an NDA with ULi for the documentation or I suspect you can
program the APIC or EISA level registers to match assuming its a PCI like
bridge.

> So.. to workaround the issue IDE interrupt handler should re-check for
> any pending IRQs. This isn't bulletproof solution, but it works and this
> is the best one we can do.

That really does not belong in a mainstream tree.

Alan
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