tree 27284a30e0b3267d4ddc7817a0fb5eb1107468a3
parent d45a9a6d80b8172e8d1c7b3019dc6d75d23e3547
author Shawn McCarney <shawnmm@us.ibm.com> 1576088769 -0600
committer Shawn McCarney <shawnmm@us.ibm.com> 1576190900 -0600

i2c: Cache adapter functionality

Enhance the I2CDevice class to cache the I2C adapter functionality
value.  The adapter functionality value should not change while the
device interface is open.

Caching the functionality value will reduce the number of ioctl() calls
by 50% when doing long sequences of I2C operations.

Tested:
* Verified adapter functionality value is cached
* Verified read() method works on a Witherspoon
* Verified close() method discards the cached functionality value

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: I2b17d91ae4e21aaf52cd4cec9eddb5aab7be37e5