On Fri, 8 Feb 2008, David Brownell wrote: > On Thursday 31 January 2008, Guennadi Liakhovetski wrote: > > As discussed on i2c mailing list with David Brownell, and number > > outside of the 0...MAX_INT range is invalid as a GPIO number. > > Define a macro, similar to NO_IRQ, to be used as a deliberate > > invalid GPIO, rather than defining a is_valid_gpio() macro. > > Actually I thought that what you needed was an is_valid_gpio(); > your motivation was that you needed a predicate. > > The problem I have with a #define for a single such invalid GPIO > number is that people will inevitably start to assume it's the > only such number. In particular "if (gpio == NO_GPIO) ..." > is by definition incorrect. > > So I'd really rather see a predicate like is_valid_gpio(). > > If you want to designate one value for use as an initializer, > then I'd rather see a simple > > #define NO_GPIO (-EINVAL) > > without any option for arch-specific overrides ... along with a > comment that this is only *one* of the numerous values which > will fail is_valid_gpio().
I was thinking about irq numbers and trying to avoid as early as possible their problem: namely that each and every platform has its own idea of which irq numbers are valid and which are not, some use 0 as invalid irq, some -1, some 256, etc. And when those platforms share drivers, problems arise. And the simple and efficient NO_IRQ notion, that would fis those problems nicely, cannot seem to establish itself. The disadvantages I see in your suggestions are: 1. two accessors (is_valid_gpio() and NO_GPIO) instead of one 2. have to include errno.h 3. it doesn't seem very logical to me to define a gpio number in terms of an error code 4. "confusing freedom" - NO_GPIO is the invalid gpio number, but, in fact, you can use just any negative number Advantages of my proposal: 1. simplicity - only one macro, and "well-definedness" - use this and only this as invalid gpio number. The rest are either valid, or undefined. 2. overridable by platforms - though I don't have any examples at hand, I can imagine, that some platforms would prefer some specific "natural" for them numbers. But, this is not something I would spend too much energy arguing about, and this is your code in the end:-) So, if you still disagree, I'll do it the way you suggest. I might well be wrong too:-) Thanks Guennadi --- Guennadi Liakhovetski -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
