[PATCH v2 2/2] ASoC: tegra: Fix redundant PLLA and PLLA_OUT0 updates

[Sameer Pujar <spujar@nvidia.com>]

Tegra audio graph card has many DAI links which connects internal
AHUB modules and external audio codecs. Since these are DPCM links,
hw_params() call in the machine driver happens for each connected
BE link and PLLA is updated every time. This is not really needed
for all links as only I/O link DAIs derive respective clocks from
PLLA_OUT0 and thus from PLLA. Hence add checks to limit the clock
updates to DAIs over I/O links.

This found to be fixing a DMIC clock discrepancy which is suspected
to happen because of back to back quick PLLA and PLLA_OUT0 rate
updates. This was observed on Jetson TX2 platform where DMIC clock
ended up with unexpected value.

Fixes: 202e2f774543 ("ASoC: tegra: Add audio graph based card driver")
Cc: stable@vger.kernel.org
Signed-off-by: Sameer Pujar <spujar@nvidia.com>
---
 sound/soc/tegra/tegra_audio_graph_card.c | 30 ++++++++++++++----------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/sound/soc/tegra/tegra_audio_graph_card.c b/sound/soc/tegra/tegra_audio_graph_card.c
index 1f2c5018bf5a..4737e776d383 100644
--- a/sound/soc/tegra/tegra_audio_graph_card.c
+++ b/sound/soc/tegra/tegra_audio_graph_card.c
@@ -10,6 +10,7 @@
 #include <linux/platform_device.h>
 #include <sound/graph_card.h>
 #include <sound/pcm_params.h>
+#include <sound/soc-dai.h>
 
 #define MAX_PLLA_OUT0_DIV 128
 
@@ -44,6 +45,21 @@ struct tegra_audio_cdata {
 	unsigned int plla_out0_rates[NUM_RATE_TYPE];
 };
 
+static bool need_clk_update(struct snd_soc_dai *dai)
+{
+	if (snd_soc_dai_is_dummy(dai) ||
+	    !dai->driver->ops ||
+	    !dai->driver->name)
+		return false;
+
+	if (strstr(dai->driver->name, "I2S") ||
+	    strstr(dai->driver->name, "DMIC") ||
+	    strstr(dai->driver->name, "DSPK"))
+		return true;
+
+	return false;
+}
+
 /* Setup PLL clock as per the given sample rate */
 static int tegra_audio_graph_update_pll(struct snd_pcm_substream *substream,
 					struct snd_pcm_hw_params *params)
@@ -140,19 +156,7 @@ static int tegra_audio_graph_hw_params(struct snd_pcm_substream *substream,
 	struct snd_soc_dai *cpu_dai = asoc_rtd_to_cpu(rtd, 0);
 	int err;
 
-	/*
-	 * This gets called for each DAI link (FE or BE) when DPCM is used.
-	 * We may not want to update PLLA rate for each call. So PLLA update
-	 * must be restricted to external I/O links (I2S, DMIC or DSPK) since
-	 * they actually depend on it. I/O modules update their clocks in
-	 * hw_param() of their respective component driver and PLLA rate
-	 * update here helps them to derive appropriate rates.
-	 *
-	 * TODO: When more HW accelerators get added (like sample rate
-	 * converter, volume gain controller etc., which don't really
-	 * depend on PLLA) we need a better way to filter here.
-	 */
-	if (cpu_dai->driver->ops && rtd->dai_link->no_pcm) {
+	if (need_clk_update(cpu_dai)) {
 		err = tegra_audio_graph_update_pll(substream, params);
 		if (err)
 			return err;
-- 
2.17.1