ASoC: tegra20: ac97: Add reset control

Tegra20 AC97 driver doesn't manage the AC97 controller reset, relying on
implicit deassertion of the reset by tegra-clk driver, which needs to be
fixed since this behaviour is unacceptable by other Tegra drivers. Add
explicit reset control to the Tegra20 AC97 driver.

Note that AC97 reset was always specified in Tegra20 device-tree, hence
DTB ABI changes aren't required.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Link: https://lore.kernel.org/r/20210314154459.15375-2-digetx@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/tegra/tegra20_ac97.c

@@ -21,6 +21,7 @@
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 #include <linux/regmap.h>
+#include <linux/reset.h>
 #include <linux/slab.h>
 #include <sound/core.h>
 #include <sound/pcm.h>
@@ -313,6 +314,12 @@ static int tegra20_ac97_platform_probe(struct platform_device *pdev)
 	}
 	dev_set_drvdata(&pdev->dev, ac97);
 
+	ac97->reset = devm_reset_control_get_exclusive(&pdev->dev, "ac97");
+	if (IS_ERR(ac97->reset)) {
+		dev_err(&pdev->dev, "Can't retrieve ac97 reset\n");
+		return PTR_ERR(ac97->reset);
+	}
+
 	ac97->clk_ac97 = devm_clk_get(&pdev->dev, NULL);
 	if (IS_ERR(ac97->clk_ac97)) {
 		dev_err(&pdev->dev, "Can't retrieve ac97 clock\n");
@@ -364,12 +371,26 @@ static int tegra20_ac97_platform_probe(struct platform_device *pdev)
 	ac97->playback_dma_data.addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
 	ac97->playback_dma_data.maxburst = 4;
 
+	ret = reset_control_assert(ac97->reset);
+	if (ret) {
+		dev_err(&pdev->dev, "Failed to assert AC'97 reset: %d\n", ret);
+		goto err_clk_put;
+	}
+
 	ret = clk_prepare_enable(ac97->clk_ac97);
 	if (ret) {
 		dev_err(&pdev->dev, "clk_enable failed: %d\n", ret);
 		goto err_clk_put;
 	}
 
+	usleep_range(10, 100);
+
+	ret = reset_control_deassert(ac97->reset);
+	if (ret) {
+		dev_err(&pdev->dev, "Failed to deassert AC'97 reset: %d\n", ret);
+		goto err_clk_disable_unprepare;
+	}
+
 	ret = snd_soc_set_ac97_ops(&tegra20_ac97_ops);
 	if (ret) {
 		dev_err(&pdev->dev, "Failed to set AC'97 ops: %d\n", ret);

sound/soc/tegra/tegra20_ac97.h

@@ -78,6 +78,7 @@ struct tegra20_ac97 {
 	struct clk *clk_ac97;
 	struct snd_dmaengine_dai_dma_data capture_dma_data;
 	struct snd_dmaengine_dai_dma_data playback_dma_data;
+	struct reset_control *reset;
 	struct regmap *regmap;
 	int reset_gpio;
 	int sync_gpio;