Messages in this thread | | | From | Eric Miao <> | Date | Tue, 7 Sep 2010 12:19:23 +0800 | Subject | Re: [PATCH] pio: add arch specific gpio_is_valid() function |
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On Tue, Sep 7, 2010 at 12:07 PM, Ryan Mallon <ryan@bluewatersys.com> wrote: > On 09/07/2010 03:54 PM, Eric Miao wrote: >> On Tue, Sep 7, 2010 at 10:44 AM, Ryan Mallon <ryan@bluewatersys.com> wrote: >>> On 09/07/2010 02:23 PM, David Brownell wrote: >>>> Still not liking or accepting this proposed >>>> change to the GPIO framework. >>>> >>>> For the AT91 case (where integers 0..N are >>>> IRQs, but N..max are GPIOs) >>>> >>>> A simpler solution is just to use a bit in >>>> the integer to indicate IRQ vs GPIO. Like >>>> maybe the sign bit.. which is never set on >>>> valid GPIO numbers, but platforms could let >>>> be set on IRQs. >>>> >>> How about this approach instead? >>> >> >> This doesn't solve the problem with more complicated settings, e.g. >> some GPIOs within are not valid, not just the begining ones. > > Agreed, but this does solve the immediate problem for AT91 in a simple > way. Are there boards in the kernel which have holes in the gpio layout? > > Another possible solution is to loop through all the gpio_chips to see > if the number maps to a valid gpio. The obvious downside to this > approach is that the complexity of gpio_is_valid becomes reasonably high > for something which should be a very simple test and, as you say below, > we probably just don't need that fine-grained information. > >> So the real question here is the semantics of gpio_is_valid(). I'd >> personally incline it reads as if a GPIO _number_ is valid generally, >> (e.g. like -1 is not a valid GPIO number), instead of that specific >> GPIO is valid on that specific platform. The latter can be judged >> with gpio_request(). > > Some drivers in the kernel appear to be using this behaviour to have > optional gpios, ie setting the foo_gpio = -1 in the platform data for > some driver. The documentation also suggests that this is what > gpio_is_valid is intended for. However, the documentation also says we > may want gpio_is_valid to return invalid on some other numbers.
Right. So I'd really like David to make the semantics clear. My intention is to keep gpio_is_valid() as simple as checking a general range to rule out most invalid cases. And just use gpio_request() to handle the platform specific cases.
> > ~Ryan > > -- > Bluewater Systems Ltd - ARM Technology Solution Centre > > Ryan Mallon 5 Amuri Park, 404 Barbadoes St > ryan@bluewatersys.com PO Box 13 889, Christchurch 8013 > http://www.bluewatersys.com New Zealand > Phone: +64 3 3779127 Freecall: Australia 1800 148 751 > Fax: +64 3 3779135 USA 1800 261 2934 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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