From: "Maciej W. Rozycki" <macro@orcam.me.uk>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: netdev@vger.kernel.org, linux-mips@vger.kernel.org,
Jakub Kicinski <kuba@kernel.org>,
Andrew Lunn <andrew+netdev@lunn.ch>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Paolo Abeni <pabeni@redhat.com>
Subject: Re: [PATCH net-next v2] declance: Remove IRQF_ONESHOT
Date: Thu, 7 May 2026 12:45:22 +0100 (BST) [thread overview]
Message-ID: <alpine.DEB.2.21.2605071211350.46195@angie.orcam.me.uk> (raw)
In-Reply-To: <20260507073427.atoJ5zsY@linutronix.de>
On Thu, 7 May 2026, Sebastian Andrzej Siewior wrote:
> > The interrupt is exceedingly rare, I've only seen it actually fire maybe
> > a dozen times across all my systems in 25+ years. It happens when there
> > is a memory read error on DMA, such as an uncorrected ECC or parity error
> > (depending on the system variant), or a bus timeout.
>
> I assumed you have other interrupts on that hw, cascaded/ operating the
> same way. But otherwise…
Hardware does have such stuff, but we don't make use of any other sources
right now.
We don't use DMA with the SCC serial ports -- I've had plans to wire that
even for asynchronous operation, because with the 3-entry only input FIFO
it's quite easy for characters to get lost at higher baud rates; we have
no driver support for the synchronous modes with these systems although
hardware has all the necessary circuitry and external port connections.
And the driver for the ESP SCSI interface was sadly lost in a conversion
many years ago when I got stuck due to a peculiarity with the hardware and
never completed it, which is a shame, but there you go -- I still hope to
do that one day, and that I consider much higher priority than DMA for the
SCC.
Another system model, the Personal DECstation, also has ISDN and sound
interfaces wired for DMA, but no driver was ever written/ported for either
and no one running Linux seems to have a specimen available anymore. I
think NetBSD guys have full support for that system.
So yeah, right now it's only LANCE that makes use of any of the DMA IRQs,
and it's actually the least complext arrangement of all the devices: LANCE
makes use of 1 DMA IRQ, ESP makes use of 3 and the SCC ports make use of 4
each. Each has one IRQ dedicated to memory read errors, and ESP and SCC
also have one each for overrun errors. The remaining IRQs are for regular
DMA operation, i.e. buffer flipping, which LANCE does not do as it makes
use of the usual DMA descriptor ring arrangement instead.
Maciej
next prev parent reply other threads:[~2026-05-07 11:45 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-27 13:53 [PATCH net-next v2] declance: Remove IRQF_ONESHOT Sebastian Andrzej Siewior
2026-01-27 15:46 ` Maciej W. Rozycki
2026-01-27 16:54 ` Sebastian Andrzej Siewior
2026-01-27 18:35 ` Maciej W. Rozycki
2026-03-29 20:27 ` Maciej W. Rozycki
2026-05-04 22:35 ` Maciej W. Rozycki
2026-05-05 7:29 ` Sebastian Andrzej Siewior
2026-05-05 12:02 ` Maciej W. Rozycki
2026-05-05 12:32 ` Sebastian Andrzej Siewior
2026-05-05 14:00 ` Maciej W. Rozycki
2026-05-05 15:24 ` Sebastian Andrzej Siewior
2026-05-06 9:25 ` Maciej W. Rozycki
2026-05-07 7:34 ` Sebastian Andrzej Siewior
2026-05-07 11:45 ` Maciej W. Rozycki [this message]
2026-01-29 3:50 ` patchwork-bot+netdevbpf
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