On 16/10/12 10:31, Roland Stigge wrote:

The recurring task of providing simultaneous access to GPIO lines (especially
for bit banging protocols) needs an appropriate API.

This patch adds a kernel internal "Block GPIO" API that enables simultaneous
access to several GPIOs. This is done by abstracting GPIOs to an n-bit word:
Once requested, it provides access to a group of GPIOs which can range over
multiple GPIO chips.

Signed-off-by: Roland Stigge <redacted>
---

<snip>

+This creates a new block of GPIOs as a list of GPIO numbers with the specified
+size which are accessible via the returned struct gpio_block and the accessor
+functions described below. Please note that you need to request the GPIOs
+separately via gpio_request(). An arbitrary list of globally valid GPIOs can be
+specified, even ranging over several gpio_chips. Actual handling of I/O
+operations will be done on a best effort base, i.e. simultaneous I/O only where
+possible by hardware and implemented in the respective GPIO driver. The number
+of GPIOs in one block is limited to 32 on a 32 bit system, and 64 on a 64 bit
+system. However, several blocks can be defined at once.

This should probably say that the number of gpios in a block is limited
to sizeof(unsigned long) or BITS_PER_LONG. I think sizeof(unsigned long)
== 8 on some 32 bit architectures.

~Ryan