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    SubjectRe: [PATCH 0/3] capebus moving omap_devices to mach-omap2
    Hi,

    On Fri, Nov 02, 2012 at 02:42:51AM -0700, Russ Dill wrote:
    > >> browse through various detect functions, yes, some of them key off an
    > >> ID, but a lot of them just check various registers to see if certain
    > >> bits are zero, or certain bits are one. A lot of I²C devices I've
    > >> dealt with have no good way of probing them, especially GPIO chips
    > >> (you'll notice none of the I²C GPIO expanders have detect functions)
    > >
    > > it doesn't mean it can't be done.
    >
    > Really? Please, do tell how you would write a detect function for a
    > PCA9534. It has 4 registers, an input port registers, an output port
    > register, a polarity inversion register, and a configuration register.

    read them and match to their reset values, perhaps ?

    > And don't forget, since we are probing, every detect routine for every
    > I²C driver will have to run with every I²C address on every bus,
    > possibly with both address formats.

    not *every* I2C address. What you say is wrong, a ->detect() method will
    only run for those addresses which the device can actually assume.

    > >> On top of all this the detect routine does not tell you if the alert
    > >> pin is connected to some IRQ, or in the case of a GPIO expander, what
    > >> those GPIOs are connected to, etc, etc.
    > >
    > > so what ? All you want to do with detect is figure out if the far end is
    > > who you think it is, not what it's doing.
    >
    > If we already knew who was there, we wouldn't need a detect routine.

    of course not :-) But the whole discussion has been about not knowing
    which capes (and thus which devices) are attached to the bone.

    --
    balbi
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