linux-kernel - Re: [PATCH v2 2/2] can: m_can: fix missed interrupts with m_can

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Message-ID: <20240923-honored-ant-of-ecstasy-f7edae-mkl@pengutronix.de>
Date: Mon, 23 Sep 2024 12:17:38 +0200
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc: Chandrasekar Ramakrishnan <rcsekar@...sung.com>, 
	Vincent Mailhol <mailhol.vincent@...adoo.fr>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Martin Hundebøll <martin@...nix.com>, 
	Markus Schneider-Pargmann <msp@...libre.com>, "Felipe Balbi (Intel)" <balbi@...nel.org>, 
	Raymond Tan <raymond.tan@...el.com>, Jarkko Nikula <jarkko.nikula@...ux.intel.com>, 
	linux-can@...r.kernel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux@...tq-group.com, lst@...gutronix.de
Subject: Re: [PATCH v2 2/2] can: m_can: fix missed interrupts with m_can_pci

On 19.09.2024 13:27:28, Matthias Schiffer wrote:
> The interrupt line of PCI devices is interpreted as edge-triggered,
> however the interrupt signal of the m_can controller integrated in Intel
> Elkhart Lake CPUs appears to be generated level-triggered.
> 
> Consider the following sequence of events:
> 
> - IR register is read, interrupt X is set
> - A new interrupt Y is triggered in the m_can controller
> - IR register is written to acknowledge interrupt X. Y remains set in IR
> 
> As at no point in this sequence no interrupt flag is set in IR, the
> m_can interrupt line will never become deasserted, and no edge will ever
> be observed to trigger another run of the ISR. This was observed to
> result in the TX queue of the EHL m_can to get stuck under high load,
> because frames were queued to the hardware in m_can_start_xmit(), but
> m_can_finish_tx() was never run to account for their successful
> transmission.
> 
> To fix the issue, repeatedly read and acknowledge interrupts at the
> start of the ISR until no interrupt flags are set, so the next incoming
> interrupt will also result in an edge on the interrupt line.
> 
> Fixes: cab7ffc0324f ("can: m_can: add PCI glue driver for Intel Elkhart Lake")
> Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>

My coworker Lucas pointed me to:

| https://wiki.linuxfoundation.org/networking/napi#non-level_sensitive_irqs

On the other hand, I would also like to convert the !peripteral part of
the driver to rx-offload. However, I am still looking for potential
customers for this task. I have talked to some TI and ST people at LPC,
maybe they are interested.

I think let's first fix edge sensitive IRQs, then rework the driver to
rx-offload.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
Vertretung Nürnberg              | Phone: +49-5121-206917-129 |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-9   |

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