[alsa-devel] [PATCH] ASoC: arizona: Add 32uS delay after putting FLL into freerun
When switching between two clock sources using the FLL freerun to smooth the transition we should wait 32uS after putting the FLL into freerun before we proceed. In practice we appear to be getting enough delay from the surrounding code, but better to make it explicit.
Signed-off-by: Charles Keepax ckeepax@opensource.wolfsonmicro.com --- sound/soc/codecs/arizona.c | 1 + 1 files changed, 1 insertions(+), 0 deletions(-)
diff --git a/sound/soc/codecs/arizona.c b/sound/soc/codecs/arizona.c index e76ecc7..8cd448c 100644 --- a/sound/soc/codecs/arizona.c +++ b/sound/soc/codecs/arizona.c @@ -2215,6 +2215,7 @@ static int arizona_enable_fll(struct arizona_fll *fll) regmap_update_bits_async(fll->arizona->regmap, fll->base + 1, ARIZONA_FLL1_FREERUN, ARIZONA_FLL1_FREERUN); + udelay(32); }
/*
On Thu, Nov 26, 2015 at 02:03:20PM +0000, Charles Keepax wrote:
When switching between two clock sources using the FLL freerun to smooth the transition we should wait 32uS after putting the FLL into freerun before we proceed. In practice we appear to be getting enough delay from the surrounding code, but better to make it explicit.
You'll almost certainly get 32us from just setting up the I/O and also...
+++ b/sound/soc/codecs/arizona.c @@ -2215,6 +2215,7 @@ static int arizona_enable_fll(struct arizona_fll *fll) regmap_update_bits_async(fll->arizona->regmap, fll->base + 1, ARIZONA_FLL1_FREERUN, ARIZONA_FLL1_FREERUN);
udelay(32);
...this won't do what you say it will - the I/O is asynchronous so what this will do is add a delay immediately after scheduling the I/O while the I/O is at best in progress and most likely before it is ever begun. You'd need to make the I/O synchronous to actually introduce the delay.
On Fri, Nov 27, 2015 at 12:26:27PM +0000, Mark Brown wrote:
On Thu, Nov 26, 2015 at 02:03:20PM +0000, Charles Keepax wrote:
When switching between two clock sources using the FLL freerun to smooth the transition we should wait 32uS after putting the FLL into freerun before we proceed. In practice we appear to be getting enough delay from the surrounding code, but better to make it explicit.
You'll almost certainly get 32us from just setting up the I/O and also...
+++ b/sound/soc/codecs/arizona.c @@ -2215,6 +2215,7 @@ static int arizona_enable_fll(struct arizona_fll *fll) regmap_update_bits_async(fll->arizona->regmap, fll->base + 1, ARIZONA_FLL1_FREERUN, ARIZONA_FLL1_FREERUN);
udelay(32);...this won't do what you say it will - the I/O is asynchronous so what this will do is add a delay immediately after scheduling the I/O while the I/O is at best in progress and most likely before it is ever begun. You'd need to make the I/O synchronous to actually introduce the delay.
Oops.. missed that, apologies I will respin.
Thanks, Charles
participants (2)
-
Charles Keepax -
Mark Brown