Re: [PATCH RFC can-next 3/3] can: tcan4x5x: add handle_dev_interrupts callback to ops

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 14.05.2021 15:51:01, Torin Cooper-Bennun wrote:
> On Fri, May 14, 2021 at 04:10:12PM +0200, Marc Kleine-Budde wrote:
> > For new code, please don't wrap the regmap_*() functions so that the
> > error values are ignored. I know, it's a bit annoying to always do the
> > "if (err) return err" dance.
> 
> Will do, thanks.
> 
> > As this is the interrupt handler there's not much we can do in case of
> > an error. In the mcp251xfd driver I print an error message and shut down
> > the interface. You should at least print an error message at the end of
> > the handle_interrupts() function.
> 
> I assume you mean the handling of errors out of aforementioned
> regmap_*() functions specifically?

ACK, I'm talking about the return value of the regmap_() functions.

> I agree we should shut down the interface - I've previously endured
> serious debugging pain due to SPI errors going unrecognised and
> causing havoc.

You can eventually do the same, return negative error value from the
tcan4x5x handler and the main IRQ handler will shut down the chip. A
return value >= 0 would be the IRQ_*.

Some background information:

You have to keep in mind, the regmap_() functions might fail due to a
non permanent problem, e.g. resource shortage (out-of-memory, etc...). I
decided it's too complicated to properly recover from those, especially
if the driver touches some FIFO pointer.

The mcp251xfd chip offers CRC check summing during read. If the driver
detect a CRC read error (that stays even after some retries), I let the
regmap_read() function to return an error that is then passed down the
call stack. And then chip will be shut down.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
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