Messages in this thread | | | Date | Tue, 18 Jan 2022 13:08:06 +0100 | From | Uwe Kleine-König <> | Subject | Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional |
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Hello Geert,
On Tue, Jan 18, 2022 at 10:37:25AM +0100, Geert Uytterhoeven wrote: > On Tue, Jan 18, 2022 at 10:09 AM Uwe Kleine-König > <u.kleine-koenig@pengutronix.de> wrote: > > For the (clk|gpiod|regulator)_get_optional() you don't have to check > > against the magic not-found value (so no implementation detail magic > > leaks into the caller code) and just pass it to the next API function. > > (And my expectation would be that if you chose to represent not-found by > > (void *)66 instead of NULL, you won't have to adapt any user, just the > > framework internal checks. This is a good thing!) > > Ah, there is the wrong assumption: drivers sometimes do need to know > if the resource was found, and thus do need to know about (void *)66, > -ENODEV, or -ENXIO. I already gave examples for IRQ and clk before. > I can imagine these exist for gpiod and regulator, too, as soon as > you go beyond the trivial "enable" and "disable" use-cases.
My premise is that every user who has to check for "not found" explicitly should not use (clk|gpiod)_get_optional() but (clk|gpiod)_get() and do proper (and explicit) error handling for -ENODEV. (clk|gpiod)_get_optional() is only for these trivial use-cases.
> And 0/NULL vs. > 0 is the natural check here: missing, but not > an error.
For me it it 100% irrelevant if "not found" is an error for the query function or not. I just have to be able to check for "not found" and react accordingly.
And adding a function
def platform_get_irq_opional(): ret = platform_get_irq() if ret == -ENXIO: return 0 return ret
it's not a useful addition to the API if I cannot use 0 as a dummy because it doesn't simplify the caller enough to justify the additional function.
The only thing I need to be able is to distinguish the cases "there is an irq", "there is no irq" and anything else is "there is a problem I cannot handle and so forward it to my caller". The semantic of platform_get_irq() is able to satisfy this requirement[1], so why introduce platform_get_irq_opional() for the small advantage that I can check for not-found using
if (!irq)
instead of
if (irq != -ENXIO)
? The semantic of platform_get_irq() is easier ("Either a usable non-negative irq number or a negative error number") compared to platform_get_irq_optional() ("Either a usable positive irq number or a negative error number or 0 meaning not found"). Usage of platform_get_irq() isn't harder or more expensive (neither for a human reader nor for a maching running the resulting compiled code). For a human reader
if (irq != -ENXIO)
is even easier to understand because for
if (!irq)
they have to check where the value comes from, see it's platform_get_irq_optional() and understand that 0 means not-found.
This function just adds overhead because as a irq framework user I have to understand another function. For me the added benefit is too small to justify the additional function. And you break out-of-tree drivers. These are all no major counter arguments, but as the advantage isn't major either, they still matter.
Best regards Uwe
[1] the only annoying thing is the error message.
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ | [unhandled content-type:application/pgp-signature] | |