On Sat, Jan 15, 2022 at 9:22 PM Sergey Shtylyov <s.shtylyov@xxxxxx> wrote: > On 1/14/22 11:22 PM, Uwe Kleine-König wrote: > > You have to understand that for clk (and regulator and gpiod) NULL is a > > valid descriptor that can actually be used, it just has no effect. So > > this is a convenience value for the case "If the clk/regulator/gpiod in > > question isn't available, there is nothing to do". This is what makes > > clk_get_optional() and the others really useful and justifies their > > existence. This doesn't apply to platform_get_irq_optional(). > > I do understand that. However, IRQs are a different beast with their > own justifications... > > clk_get_optional() is sane and sensible for cases where the clk might be > > absent and it helps you because you don't have to differentiate between > > "not found" and "there is an actual resource". > > > > The reason for platform_get_irq_optional()'s existence is just that > > platform_get_irq() emits an error message which is wrong or suboptimal > > I think you are very wrong here. The real reason is to simplify the > callers. Indeed. Even for clocks, you cannot assume that you can always blindly use the returned dummy (actually a NULL pointer) to call into the clk API. While this works fine for simple use cases, where you just want to enable/disable an optional clock (clk_prepare_enable() and clk_disable_unprepare()), it does not work for more complex use cases. Consider a device with multiple clock inputs, some of them optional, where the device driver has to find, select and configure a suitable clock to operate at a certain clock frequency. The driver can call clk_get_rate(NULL) fine, but will always receive a zero rate, so it has to check for this (regardless of this being a dummy clock or not, because this could be an unpopulated clock crystal, which would be described in DT as a (present) fixed-rate clock with clock-frequency = <0>). For configuring the clock rate, the driver does need to check explicitly for the presence of a dummy clock, as clk_set_rate(NULL, rate) returns 0 ("success"), while obviously it didn't do anything, and thus configuring the device to use that clock would cause breakage. You can check if the clock is a real clock or a dummy using "if (clk) ...". And you'd use the same pattern with platform_irq_get_optional() if it would return 0 if the IRQ was not found: "if (irq) ...". Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds