David Brownell wrote:
On Monday 20 November 2006 7:44 pm, Bill Gatliff wrote:
So, you're saying that if GPIOA1 can come out on pins ZZ1 and BB6, then
there would be two unique "GPIO numbers", one for each possibility?
No; one number, since it's controlled by the same set of bits in the GPIO
controller (e.g. bit 12 in the registers of bank 3) regardless of how the
signals are routed out through pins. That's my point: GPIO number need
not imply a particular pin, and vice versa.
Ok, thanks for the OMAP stuff. I think I can understand now.
Why not have GPIO numbers refer to unique combinations of GPIO+pin? If
the GPIO line is tied to a piece of external hardware, that connection
is surely through a specific pin. So it seems like you'd need GPIO+pin
every time there was an option.
So regardless of whether GPIO_62 is routed to ball M7 or G20, it's still
going to use number 62, which is bit 14 in various registers of the GPIO4
module, starting at 0xfffbb400 ... and for good fun, the muxing API will
refer to the balls on the (smaller) ZZG package even if your board uses
the larger ZDY package (so your schematics might say J5 not M7, that table
is very handy in such cases).
Yikes! :)
Explain to me why having GPIO enumerations map to unique GPIO+pin
combinations would be a bad idea in this case? It seems like the point
here is to help a driver find and assert their GPIO _pin_ so that the
driver can can talk to the attached external hardware. Having an
enumeration "GPIO62M7" would be a handy way to do that. Maybe the
enumeration is actually defined as ((0x400 << 16) | (14 << 8) | 4), or
some other encoding that makes it easy in the implementation of
gpio_XXX() to find the right registers and get the routing set up
correctly. It's just an opaque, magic number to the driver after all.
And since GPIOs are arch/mach/board-specific anyway, who would care if
OMAP was the only system that had an enumeration called "GPIO62M7"?
When other boards set up their platform_struct, they'd use the
enumerations available for that platform. "GPIOA1" in systems where
that GPIO line could only go to one pin per the datasheet, for example.
b.g.
--
Bill Gatliff
[email protected]
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