Comment 2 for bug 1448830

There is a regmap fix which is mandatory to the latest alsa driver, but this fix is not in the trusty kernel. The regmap fix is as below:

 commit 4ceba98d3fe204c59e5f63c4d834b45dcfe789f0
Author: Takashi Iwai <email address hidden>
Date: Wed Mar 4 15:29:17 2015 +0100

    regmap: Skip read-only registers in regcache_sync()

    regcache_sync() spews warnings when a value was cached for a read-only
    register as it tries to write all registers no matter whether they are
    writable or not. This patch adds regmap_wrtieable() checks for
    avoiding it in regcache_sync_block_single() and regcache_block_raw().

    Signed-off-by: Takashi Iwai <email address hidden>
    Signed-off-by: Mark Brown <email address hidden>

diff --git a/drivers/base/regmap/regcache.c b/drivers/base/regmap/regcache.c
index f373c35..da84f54 100644
--- a/drivers/base/regmap/regcache.c
+++ b/drivers/base/regmap/regcache.c