serial: max310x: improve crystal stable clock detection

Some people are seeing a warning similar to this when using a crystal:

    max310x 11-006c: clock is not stable yet

The datasheet doesn't mention the maximum time to wait for the clock to be
stable when using a crystal, and it seems that the 10ms delay in the driver
is not always sufficient.

Jan Kundrát reported that it took three tries (each separated by 10ms) to
get a stable clock.

Modify behavior to check stable clock ready bit multiple times (20), and
waiting 10ms between each try.

Note: the first draft of the driver originally used a 50ms delay, without
checking the clock stable bit.
Then a loop with 1000 retries was implemented, each time reading the clock
stable bit.

Fixes: 4cf9a888fd3c ("serial: max310x: Check the clock readiness")
Cc: [email protected]
Suggested-by: Jan Kundrát <[email protected]>
Link: https://www.spinics.net/lists/linux-serial/msg35773.html
Link: https://lore.kernel.org/all/[email protected]/raw
Link: https://github.com/boundarydevices/linux/commit/e5dfe3e4a751392515d78051973190301a37ca9a
Signed-off-by: Hugo Villeneuve <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

0 files changed, 0 insertions, 0 deletions