On 27.07.2021 12:47:17, Manivannan Sadhasivam wrote: > On Sat, Jul 24, 2021 at 10:52:13PM +0200, Marc Kleine-Budde wrote: > > The driver's IRQ handler supports shared IRQs, so request a shared IRQ > > handler. > > I don't see any issue with the idea but I'd like to understand the > requirement for it. Hardware designers might come up with strange ideas, so better be prepared for this. :) But seriously, there's a group of people trying to bring the mcp251xfd driver to work on ACPI based systems. Having a shared mcp251xfd IRQ handler will (hopefully) help them during debugging. I've written the IRQ handler to properly only return IRQ_HANDLED if there really was an interrupt, this means it should be capable running as a shared IRQ handler. I've tested it and it works. So let the driver request a shared IRQ handler. > Usually the IRQ lines are shared when multiple devices use them > physically. For instance, a MFD device using a single GPIO for all of its > functions. But I don't see any sort of requirement like that here. Indeed there is really no good reason to do so, but it works. For testing I've connected 2 mcp2518fd to the same IRQ line and the kernel runs both IRQ handlers an interrupt is triggered. If course this brings the overhead of an additional SPI transfer per IRQ, but it works. > Making the IRQ lines shared will only induce latency IMO. ACK - you will not get better performance compared to separate IRQ lines :) But if you don't use shared interrupts this change doesn't make the driver or system any slower or induce latency. regards, Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
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