ASoC: meson: axg-tdm-formatter: add reset

Add the optional reset line handling which is present on the new SoC
families, such as the g12a. Triggering this reset is not critical but
it helps solve a channel shift issue on the g12a.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lore.kernel.org/r/20190703120749.32341-3-jbrunet@baylibre.com
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/sound/soc/meson/axg-tdm-formatter.c b/sound/soc/meson/axg-tdm-formatter.c
index 0c6cce5c577328baefe47c9fe0448b1f46c38536..2e498201139feb4711ca74ac89f6a89eeafa4789 100644 (file)
--- a/sound/soc/meson/axg-tdm-formatter.c
+++ b/sound/soc/meson/axg-tdm-formatter.c
@@ -7,6 +7,7 @@
 #include <linux/module.h>
 #include <linux/of_platform.h>
 #include <linux/regmap.h>
+#include <linux/reset.h>
 #include <sound/soc.h>
 
 #include "axg-tdm-formatter.h"
@@ -20,6 +21,7 @@ struct axg_tdm_formatter {
        struct clk *lrclk;
        struct clk *sclk_sel;
        struct clk *lrclk_sel;
+       struct reset_control *reset;
        bool enabled;
        struct regmap *map;
 };
@@ -75,6 +77,24 @@ static int axg_tdm_formatter_enable(struct axg_tdm_formatter *formatter)
        if (formatter->enabled)
                return 0;
 
+       /*
+        * On the g12a (and possibly other SoCs), when a stream using
+        * multiple lanes is restarted, it will sometimes not start
+        * from the first lane, but randomly from another used one.
+        * The result is an unexpected and random channel shift.
+        *
+        * The hypothesis is that an HW counter is not properly reset
+        * and the formatter simply starts on the lane it stopped
+        * before. Unfortunately, there does not seems to be a way to
+        * reset this through the registers of the block.
+        *
+        * However, the g12a has indenpendent reset lines for each audio
+        * devices. Using this reset before each start solves the issue.
+        */
+       ret = reset_control_reset(formatter->reset);
+       if (ret)
+               return ret;
+
        /*
         * If sclk is inverted, invert it back and provide the inversion
         * required by the formatter
@@ -306,6 +326,15 @@ int axg_tdm_formatter_probe(struct platform_device *pdev)
                return ret;
        }
 
+       /* Formatter dedicated reset line */
+       formatter->reset = reset_control_get_optional_exclusive(dev, NULL);
+       if (IS_ERR(formatter->reset)) {
+               ret = PTR_ERR(formatter->reset);
+               if (ret != -EPROBE_DEFER)
+                       dev_err(dev, "failed to get reset: %d\n", ret);
+               return ret;
+       }
+
        return devm_snd_soc_register_component(dev, drv->component_drv,
                                               NULL, 0);
 }