On Monday 01 January 2007 12:55 pm, Pavel Machek wrote:
> > Think of it as "cookies represented by integers" if you like.
>
> typedef int gpio_t would hurt, and would serve as a useful
> documentation hint.
Yes, I agree that such needless obfuscation hurts. ;)
Plus, such a typedef would disagree with Documentation/CodingStyle
which says "... the rule should basically be to NEVER EVER use a
typedef" (with some exceptions not matched here).
> > Should it instead say that's an (obviously unchecked) error?
>
> Saying it is an error would be okay by me. (Or "Behaviour of these calls for
> GPIOs that can't be safely accessed without sleeping is undefined.").
See the appended doc patch ... better?
- Dave
================= CUT HERE
Index: at91/Documentation/gpio.txt
===================================================================
--- at91.orig/Documentation/gpio.txt 2006-12-29 00:00:28.000000000 -0800
+++ at91/Documentation/gpio.txt 2006-12-29 15:47:18.000000000 -0800
@@ -78,7 +78,8 @@ Identifying GPIOs
-----------------
GPIOs are identified by unsigned integers in the range 0..MAX_INT. That
reserves "negative" numbers for other purposes like marking signals as
-"not available on this board", or indicating faults.
+"not available on this board", or indicating faults. Code that doesn't
+touch the underlying hardware treats these integers as opaque cookies.
Platforms define how they use those integers, and usually #define symbols
for the GPIO lines so that board-specific setup code directly corresponds
@@ -139,8 +140,8 @@ issues including wire-OR and output late
The get/set calls have no error returns because "invalid GPIO" should have
been reported earlier in gpio_set_direction(). However, note that not all
platforms can read the value of output pins; those that can't should always
-return zero. Also, these calls will be ignored for GPIOs that can't safely
-be accessed wihtout sleeping (see below).
+return zero. Also, using these calls for GPIOs that can't safely be accessed
+without sleeping (see below) is an error.
Platform-specific implementations are encouraged to optimise the two
calls to access the GPIO value in cases where the GPIO number (and for
@@ -239,7 +240,8 @@ options are part of the IRQ interface, e
system wakeup capabilities.
Non-error values returned from irq_to_gpio() would most commonly be used
-with gpio_get_value().
+with gpio_get_value(), for example to initialize or update driver state
+when the IRQ is edge-triggered.
@@ -262,7 +264,8 @@ like the aforementioned options for inpu
Hardware may support reading or writing GPIOs in gangs, but that's usually
configuration dependednt: for GPIOs sharing the same bank. (GPIOs are
commonly grouped in banks of 16 or 32, with a given SOC having several such
-banks.) Code relying on such mechanisms will necessarily be nonportable.
+banks.) Some systems can trigger IRQs from output GPIOs. Code relying on
+such mechanisms will necessarily be nonportable.
Dynamic definition of GPIOs is not currently supported; for example, as
a side effect of configuring an add-on board with some GPIO expanders.
-
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/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
