Re: [PATCH v2 2/2] can: m_can: fix missed interrupts with m_can_pci

[Marc Kleine-Budde]

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@xxxxxxxxxxxxxxx>

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          |
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