On Wed, Jan 12, 2022 at 11:27:02AM +0100, Geert Uytterhoeven wrote: > Hi Uwe, > > On Wed, Jan 12, 2022 at 9:51 AM Uwe Kleine-König > <u.kleine-koenig@xxxxxxxxxxxxxx> wrote: > > On Wed, Jan 12, 2022 at 09:33:48AM +0100, Geert Uytterhoeven wrote: > > > On Mon, Jan 10, 2022 at 10:20 PM Andrew Lunn <andrew@xxxxxxx> wrote: > > > > On Mon, Jan 10, 2022 at 09:10:14PM +0100, Uwe Kleine-König wrote: > > > > > On Mon, Jan 10, 2022 at 10:54:48PM +0300, Sergey Shtylyov wrote: > > > > > > This patch is based on the former Andy Shevchenko's patch: > > > > > > > > > > > > https://lore.kernel.org/lkml/20210331144526.19439-1-andriy.shevchenko@xxxxxxxxxxxxxxx/ > > > > > > > > > > > > Currently platform_get_irq_optional() returns an error code even if IRQ > > > > > > resource simply has not been found. It prevents the callers from being > > > > > > error code agnostic in their error handling: > > > > > > > > > > > > ret = platform_get_irq_optional(...); > > > > > > if (ret < 0 && ret != -ENXIO) > > > > > > return ret; // respect deferred probe > > > > > > if (ret > 0) > > > > > > ...we get an IRQ... > > > > > > > > > > > > All other *_optional() APIs seem to return 0 or NULL in case an optional > > > > > > resource is not available. Let's follow this good example, so that the > > > > > > callers would look like: > > > > > > > > > > > > ret = platform_get_irq_optional(...); > > > > > > if (ret < 0) > > > > > > return ret; > > > > > > if (ret > 0) > > > > > > ...we get an IRQ... > > > > > > > > > > The difference to gpiod_get_optional (and most other *_optional) is that > > > > > you can use the NULL value as if it were a valid GPIO. > > > > > > > > > > As this isn't given with for irqs, I don't think changing the return > > > > > value has much sense. > > > > > > > > We actually want platform_get_irq_optional() to look different to all > > > > the other _optional() methods because it is not equivalent. If it > > > > looks the same, developers will assume it is the same, and get > > > > themselves into trouble. > > > > > > Developers already assume it is the same, and thus forget they have > > > to check against -ENXIO instead of zero. I agree that -ENXIO is unfortunate and -ENOENT would be more in line with other functions. I assume it's insane to want to change that. > > Is this an ack for renaming platform_get_irq_optional() to > > platform_get_irq_silent()? > > No it isn't ;-) > > If an optional IRQ is not present, drivers either just ignore it (e.g. > for devices that can have multiple interrupts or a single muxed IRQ), > or they have to resort to polling. For the latter, fall-back handling > is needed elsewhere in the driver. I think irq are not suitable for such a dummy handling. For clocks or GPIOs there are cases where just doing nothing in the absence of a certain optional clock or GPIO is fine. I checked a few users of platform_get_irq_optional() and I didn't find a single one that doesn't need to differentiate the irq and the no-irq case later. Do you know one? If you do, isn't that so exceptional that it doesn't justify the idea of a dummy irq value? So until proven otherwise I think platform_get_irq_optional() just isn't in the spirit of clk_get_optional() and gpiod_get_optional() because there are no use cases where a dummy value would be good enough. (Even if request_irq would be a noop for a dummy irq value.) The motivation why platform_get_irq_optional() was introduced was just that platform_get_irq() started to emit an error message (in commit 7723f4c5ecdb8d832f049f8483beb0d1081cedf6) and the (proportional) few drivers where the error message was bad needed a variant that doesn't emit the error message. Look at 31a8d8fa84c51d3ab00bf059158d5de6178cf890, the motivation to use platform_get_irq_optional() wasn't that it simplifies handling in the driver, but that it doesn't emit an error message. Or 8f5783ad9eb83747471f61f94dbe209fb9fb8a7d, or 2fd276c3ee4bd42eb034f8954964a5ae74187c6b, or 55cc33fab5ac9f7e2a97aa7c564e8b35355886d5. Just look at the output of git log -Splatform_get_irq_optional to find some more. That convinces me, that platform_get_irq_optional() is a bad name. The only difference to platform_get_irq is that it's silent. And returning a dummy irq value (which would make it aligned with the other _optional functions) isn't possible. > To me it sounds much more logical for the driver to check if an > optional irq is non-zero (available) or zero (not available), than to > sprinkle around checks for -ENXIO. In addition, you have to remember > that this one returns -ENXIO, while other APIs use -ENOENT or -ENOSYS > (or some other error code) to indicate absence. I thought not having > to care about the actual error code was the main reason behind the > introduction of the *_optional() APIs. No, the main benefit of gpiod_get_optional() (and clk_get_optional()) is that you can handle an absent GPIO (or clk) as if it were available. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |
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