linux-kernel - Re: [PATCH] m68k/mac: Avoid stuck ISM IOP interrupt on Quadra 900/950

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Date:   Mon, 25 May 2020 10:46:10 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Finn Thain <fthain@...egraphics.com.au>
Cc:     Joshua Thompson <funaho@...ai.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] m68k/mac: Avoid stuck ISM IOP interrupt on Quadra 900/950

On Wed, May 20, 2020 at 6:41 AM Finn Thain <fthain@...egraphics.com.au> wrote:
> On a Quadra 900/950, the ISM IOP IRQ output pin is connected to an
> edge-triggered input on VIA2. It is theoretically possible that this
> signal could fail to produce the expected VIA2 interrupt.
>
> The two IOP interrupt flags can be asserted in any order but the logic
> in iop_ism_irq() does not allow for that. In particular, INT0 can be
> asserted right after INT0 is checked and before INT1 is cleared.
>
> Such an interrupt would produce no new edge and VIA2 would detect no
> further interrupts from the IOP. Avoid this by looping over the INT0/1
> handlers so an edge can be produced.
>
> Cc: Joshua Thompson <funaho@...ai.org>
> Tested-by: Stan Johnson <userm57@...oo.com>
> Signed-off-by: Finn Thain <fthain@...egraphics.com.au>

Reviewed-by: Geert Uytterhoeven <geert@...ux-m68k.org>
i.e. will queue in the m68k for-v5.8 branch.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds