Messages in this thread | | | Date | Mon, 20 Nov 2006 23:09:46 -0600 | From | Bill Gatliff <> | Subject | Re: [patch/rfc 2.6.19-rc5] arch-neutral GPIO calls |
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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 bgat@billgatliff.com
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