[RFC PATCH v2 0/2] master clock issues

[RFC PATCH v2 0/2] master clock issues

[olivier moysan]

Hello,

I face two issues using wm8994 codec driver.
Below is a description of the use cases rising the problem.
I added the patches which allow to fix these issues.
These minimalist patches can be seen as a starting point for a discussion on the best
way to handle the use cases exposed.


- ASoC: wm8994: default master clock selection

Use case:
CPU DAI and codec are managed through simple card.
Wolson codec wm8994 is set as slave of CPU DAI and CPU DAI feeds codec with master clock.
Master clock is derived from mclk-fs property and provided to CPU DAI and codec 
through snd_soc_dai_set_sysclk API. 

Analysis:
The simple card assumes id 0 for master clock.
However wm8994 codec exposes master clock ids from 1 to 4. (MCLK1, MCLK2 ..)

The proposal in this patch is to define a default selection regarding master clock
when id 0 is provided.


- ASoC: wm8994: delay aifxclk activation

Use case:
Wolson codec wm8994 is set as slave of CPU DAI and CPU DAI feeds codec with master clock.
CPU DAI generates master clock when enabled in trigger callback.
So master clock is available only at runtime. 
Master clock is not available when configuring codec through alsa controls.

Analysis:
When we configure aifx clock while master clock is not active, related registers are not updated in wm8894 codec.
A way to go around this problem, is to delay aifxclk activation until SND_SOC_DAPM_POST_PMU DAPM stage.
The purpose of patch here is to illustrate this workaround. 

What I cannot clearly figure out, is  how this may impact other uses of wm8894 codec.
I try to know if it's worth investigating further in this direction or if it will not be applicable.
If not applicable, what maybe the other options ?

Changes in v2:
	Add change log on aifxclk delay patch.

regards
olivier

olivier moysan (2):
  ASoC: wm8994: default master clock selection
  ASoC: wm8994: delay aifxclk activation

 sound/soc/codecs/wm8994.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

-- 
1.9.1

[RFC PATCH v2 1/2] ASoC: wm8994: default master clock selection

[olivier moysan]

This patch allows the wm8994 codec driver to be used
with simple card when mclk fs is provided in dai link.

Signed-off-by: olivier moysan <olivier.moysan@st.com>
---
 sound/soc/codecs/wm8994.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/sound/soc/codecs/wm8994.c b/sound/soc/codecs/wm8994.c
index 3896523..ccf640a 100644
--- a/sound/soc/codecs/wm8994.c
+++ b/sound/soc/codecs/wm8994.c
@@ -2389,6 +2389,7 @@ static int wm8994_set_dai_sysclk(struct snd_soc_dai *dai,
 
 	switch (clk_id) {
 	case WM8994_SYSCLK_MCLK1:
+	default:
 		wm8994->sysclk[dai->id - 1] = WM8994_SYSCLK_MCLK1;
 		wm8994->mclk[0] = freq;
 		dev_dbg(dai->dev, "AIF%d using MCLK1 at %uHz\n",
@@ -2431,9 +2432,6 @@ static int wm8994_set_dai_sysclk(struct snd_soc_dai *dai,
 			snd_soc_update_bits(codec, WM8994_POWER_MANAGEMENT_2,
 					    WM8994_OPCLK_ENA, 0);
 		}
-
-	default:
-		return -EINVAL;
 	}
 
 	configure_clock(codec);
-- 
1.9.1

[RFC PATCH v2 2/2] ASoC: wm8994: delay aifxclk activation

[olivier moysan]

This patch is a draft.

The aim of this patch is to allow the following use case:
- The codec wm8994 is configured as a slave of CPU DAI
- The codec is configured before runtime
- CPU DAI provides master clock to the codec at runtime only

The wm8994 cannot be configured as long as master clock
is not provided to the codec.
aif clock, charge pump and DC servo registers are written
to the codec but are not read back at their expected values,
when the master clock is not set during configuration.
In this use case, master clock is not available before
pcm stream start.
So previous settings are failing
if there are set in SND_SOC_DAPM_PRE_PMU stage.

A way to go around this problem, is to delay aifxclk activation
until SND_SOC_DAPM_POST_PMU DAPM stage.
However delaying aif clock may have side effect on other use cases.

The purpose of this patch is to illustrate the principle of the fix
and to check if it may be applicable in all other contexts.


Signed-off-by: olivier moysan <olivier.moysan@st.com>
---
 sound/soc/codecs/wm8994.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/sound/soc/codecs/wm8994.c b/sound/soc/codecs/wm8994.c
index ccf640a..6782d9e 100644
--- a/sound/soc/codecs/wm8994.c
+++ b/sound/soc/codecs/wm8994.c
@@ -1262,7 +1262,7 @@ static int late_enable_ev(struct snd_soc_dapm_widget *w,
 	struct wm8994_priv *wm8994 = snd_soc_codec_get_drvdata(codec);
 
 	switch (event) {
-	case SND_SOC_DAPM_PRE_PMU:
+	case SND_SOC_DAPM_POST_PMU:
 		if (wm8994->aif1clk_enable) {
 			aif1clk_ev(w, kcontrol, SND_SOC_DAPM_PRE_PMU);
 			snd_soc_update_bits(codec, WM8994_AIF1_CLOCKING_1,
@@ -1615,6 +1615,8 @@ static SOC_ENUM_SINGLE_DECL(aif2dacr_src_enum,
 SND_SOC_DAPM_MUX_E("Right Headphone Mux", SND_SOC_NOPM, 0, 0, &wm_hubs_hpr_mux,
 		   late_enable_ev, SND_SOC_DAPM_PRE_PMU),
 
+SND_SOC_DAPM_POST("Late Enable PGA", late_enable_ev),
+
 SND_SOC_DAPM_POST("Late Disable PGA", late_disable_ev)
 };
 
-- 
1.9.1