[alsa-devel] [PATCH] ASoC: sgtl5000: add support for a fixed sysclk frequency

[Fabio Estevam]

[Sorry for the top-posting. I did not see your message in the mailing list]


Hi Jakob,


arch/arm/boot/dts/imx51-babbage.dts has SYS_MCLK generated by an external fixed oscillator and it works fine.


Do you really need this new property?

________________________________
From: Jakob Unterwurzacher <jakob.unterwurzacher at theobroma-systems.com>
Sent: Friday, October 6, 2017 5:34:44 AM
To: linux-kernel at vger.kernel.org
Cc: Jakob Unterwurzacher; Klaus Goger; Liam Girdwood; Mark Brown; Rob Herring; Mark Rutland; Jaroslav Kysela; Takashi Iwai; Richard Leitner; Fabio Estevam; Bhumika Goyal; alsa-devel at alsa-project.org; devicetree at vger.kernel.org
Subject: [PATCH] ASoC: sgtl5000: add support for a fixed sysclk frequency

The system clock, also called SYS_MCLK in the SGTL5000 datasheet,
is usually generated by the I2S master with a frequency proportional
to the sample rate.

However, this is not always the case. Compute modules following
the Qseven specification, for example, do not even have a pin for
I2S SYS_MCLK on their board-to-board connector. Only I2S_WS, I2S_RST#
I2S_CLK, I2S_SDI and I2S_SDO are specified.

Instead, SYS_MCLK is usually generated by an external fixed oscillator.

Add support for this scenario, enabled by the new "sysclk-fixed"
devicetree property.

Tested on a "Puma" RK3399-Q7 compute module with a "Haikou" baseboard
that has a fixed 24.576 MHz oscillator connected to the codec's SYS_MCLK.

Signed-off-by: Jakob Unterwurzacher <jakob.unterwurzacher at theobroma-systems.com>
Cc: Klaus Goger <klaus.goger at theobroma-systems.com>
---
 Documentation/devicetree/bindings/sound/sgtl5000.txt |  5 +++++
 sound/soc/codecs/sgtl5000.c                          | 12 ++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/Documentation/devicetree/bindings/sound/sgtl5000.txt b/Documentation/devicetree/bindings/sound/sgtl5000.txt
index 7a73a9d62015..0d0dd58b2d4a 100644
--- a/Documentation/devicetree/bindings/sound/sgtl5000.txt
+++ b/Documentation/devicetree/bindings/sound/sgtl5000.txt
@@ -35,6 +35,11 @@ VDDIO                1.8V            2.5V            3.3V
 2 =             3.33 mA         5.74 mA         8.03  mA
 3 =             4.99 mA         8.61 mA         12.05 mA

+- sysclk-fixed : If this property exists, the sysclk is considered to be
+       generated by a fixed-frequency oscillator. The frequency value is read
+       from the clock defined in the "clocks" property. set_sysclk requests
+       are ignored.
+
 Example:

 codec: sgtl5000 at 0a {
diff --git a/sound/soc/codecs/sgtl5000.c b/sound/soc/codecs/sgtl5000.c
index f2bb4feba3b6..be3aea89371c 100644
--- a/sound/soc/codecs/sgtl5000.c
+++ b/sound/soc/codecs/sgtl5000.c
@@ -133,6 +133,7 @@ struct sgtl5000_priv {
         u8 micbias_resistor;
         u8 micbias_voltage;
         u8 lrclk_strength;
+       u8 sysclk_fixed; /* sysclk rate cannot be changed */
 };

 /*
@@ -613,6 +614,10 @@ static int sgtl5000_set_dai_sysclk(struct snd_soc_dai *codec_dai,

         switch (clk_id) {
         case SGTL5000_SYSCLK:
+               if (sgtl5000->sysclk_fixed) {
+                       dev_dbg(codec->dev, "sysclk-fixed: ignoring set_sysclk request\n");
+                       return 0;
+               }
                 sgtl5000->sysclk = freq;
                 break;
         default:
@@ -1444,6 +1449,13 @@ static int sgtl5000_i2c_probe(struct i2c_client *client,
                 } else {
                         sgtl5000->micbias_voltage = 0;
                 }
+               if (of_property_read_bool(np, "sysclk-fixed")) {
+                       sgtl5000->sysclk = clk_get_rate(sgtl5000->mclk);
+                       sgtl5000->sysclk_fixed = 1;
+                       dev_dbg(&client->dev,
+                               "sysclk-fixed: setting sysclk to fixed value %d\n",
+                               sgtl5000->sysclk);
+               }
         }

         sgtl5000->lrclk_strength = I2S_LRCLK_STRENGTH_LOW;
--
2.11.0