From: Peter Maydell <peter.maydell@linaro.org>
To: BALATON Zoltan <balaton@eik.bme.hu>
Cc: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>,
qemu-ppc <qemu-ppc@nongnu.org>,
QEMU Developers <qemu-devel@nongnu.org>,
Guenter Roeck <linux@roeck-us.net>,
David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [PATCH v2 3/3] sam460ex: Clean up irq mapping
Date: Thu, 31 Dec 2020 15:11:04 +0000 [thread overview]
Message-ID: <CAFEAcA96wr_+DmXfR5ba_MEPB+sBow-QR1wpvSvKawus7qzKVg@mail.gmail.com> (raw)
In-Reply-To: <6892fc8ac57283bf7ba27fe89ea9dbdd6a37f988.1609413115.git.balaton@eik.bme.hu>
On Thu, 31 Dec 2020 at 11:20, BALATON Zoltan <balaton@eik.bme.hu> wrote:
>
> Avoid mapping multiple interrupts to the same irq. Instead map them to
> the 4 PCI interrupts and use an or-gate in the board to connect them
> to the interrupt controller. This does not fix any known problem but
> does not seem to cause a new problem either and may be cleaner at least.
>
> Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
> Tested-by: Guenter Roeck <linux@roeck-us.net>
So, this patch is a behavioural change, but I think it's
probably a change to the right behaviour. The difference
is relatively slight, but you would see it if there are two
different PCI cards and they both assert a different PCI
interrupt, and then one of them lowers the interrupt
before the other:
device A: _____|---------|________
device B: ________|----------|____
With the old code, the signal values as seen by the UIC
look like this:
UIC input: _____|---------|________
(this is because when device A says "interrupt line value 0 now"
we just pass "interrupt line value 0" through to the output).
and with an OR gate they look like:
UIC input: _____|-------------|____
(which is probably the actual behaviour -- UIC line stays
signalled until all PCI interrupts are quelled).
For this to matter to a guest it would have to be doing something
a bit odd in its interrupt handling code, though, I suspect
(like saying "stop looking for device drivers which need to
service their device once the UIC interrupt is no longer asserted").
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
thanks
-- PMM
next prev parent reply other threads:[~2020-12-31 15:12 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-31 11:11 [PATCH v2 0/3] Clean up sam460ex irq mapping BALATON Zoltan via
2020-12-25 20:12 ` [PATCH v2 2/3] sam460ex: Remove FDT_PPC dependency from KConfig BALATON Zoltan via
2020-12-31 16:08 ` Philippe Mathieu-Daudé
2021-01-04 1:51 ` BALATON Zoltan via
2021-01-04 11:48 ` Peter Maydell
2021-01-05 12:50 ` Paolo Bonzini
2020-12-31 11:11 ` [PATCH v2 1/3] ppc4xx: Move common dependency on serial to common option BALATON Zoltan via
2021-01-04 0:31 ` David Gibson
2021-01-04 1:25 ` BALATON Zoltan via
2020-12-31 11:11 ` [PATCH v2 3/3] sam460ex: Clean up irq mapping BALATON Zoltan via
2020-12-31 15:11 ` Peter Maydell [this message]
2020-12-31 15:51 ` Peter Maydell
2020-12-31 20:54 ` BALATON Zoltan via
2020-12-31 20:58 ` BALATON Zoltan via
2021-01-01 12:03 ` Peter Maydell
2021-01-03 1:46 ` BALATON Zoltan via
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