ASoC: rockchip: i2s-tdm: Strip out direct CRU use

In cases where both rx and tx lrck are synced to the same source,
the resets for rx and tx need to be triggered simultaneously,
according to the downstream driver.

As there is no reset API to atomically bulk (de)assert two resets
at once, what the driver did was implement half a reset controller
specific to Rockchip, which tried to write the registers for the
resets within one write ideally or several writes within an irqsave
section.

This of course violates abstractions quite badly. The driver should
not write to the CRU's registers directly.

In practice, for the cases I tested the driver with, which is audio
playback, replacing the synchronised asserts with just individual
ones does not seem to make any difference.

If it turns out that this breaks something in the future, it should
be fixed through the specification and implementation of an atomic
bulk reset API, not with a CRU hack.
Signed-off-by: Nicolas Frattaroli <frattaroli.nicolas@gmail.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Message-Id: <20211016105354.116513-2-frattaroli.nicolas@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/rockchip/rockchip_i2s_tdm.c

@@ -76,7 +76,6 @@ struct rk_i2s_tdm_dev {
 	struct reset_control *tx_reset;
 	struct reset_control *rx_reset;
 	struct rk_i2s_soc_data *soc_data;
-	void __iomem *cru_base;
 	bool is_master_mode;
 	bool io_multiplex;
 	bool mclk_calibrate;
@@ -92,8 +91,6 @@ struct rk_i2s_tdm_dev {
 	unsigned int i2s_sdis[CH_GRP_MAX];
 	unsigned int i2s_sdos[CH_GRP_MAX];
 	int clk_ppm;
-	int tx_reset_id;
-	int rx_reset_id;
 	int refcount;
 	spinlock_t lock; /* xfer lock */
 	bool has_playback;
@@ -222,83 +219,35 @@ static inline struct rk_i2s_tdm_dev *to_info(struct snd_soc_dai *dai)
 	return snd_soc_dai_get_drvdata(dai);
 }
 
-static void rockchip_snd_xfer_reset_assert(struct rk_i2s_tdm_dev *i2s_tdm,
-					   int tx_bank, int tx_offset,
-					   int rx_bank, int rx_offset)
-{
-	void __iomem *cru_reset;
-	unsigned long flags;
-
-	cru_reset = i2s_tdm->cru_base + i2s_tdm->soc_data->softrst_offset;
-
-	if (tx_bank == rx_bank) {
-		writel(BIT(tx_offset) | BIT(rx_offset) |
-		       (BIT(tx_offset) << 16) | (BIT(rx_offset) << 16),
-		       cru_reset + (tx_bank * 4));
-	} else {
-		local_irq_save(flags);
-		writel(BIT(tx_offset) | (BIT(tx_offset) << 16),
-		       cru_reset + (tx_bank * 4));
-		writel(BIT(rx_offset) | (BIT(rx_offset) << 16),
-		       cru_reset + (rx_bank * 4));
-		local_irq_restore(flags);
-	}
-}
-
-static void rockchip_snd_xfer_reset_deassert(struct rk_i2s_tdm_dev *i2s_tdm,
-					     int tx_bank, int tx_offset,
-					     int rx_bank, int rx_offset)
-{
-	void __iomem *cru_reset;
-	unsigned long flags;
-
-	cru_reset = i2s_tdm->cru_base + i2s_tdm->soc_data->softrst_offset;
-
-	if (tx_bank == rx_bank) {
-		writel((BIT(tx_offset) << 16) | (BIT(rx_offset) << 16),
-		       cru_reset + (tx_bank * 4));
-	} else {
-		local_irq_save(flags);
-		writel((BIT(tx_offset) << 16),
-		       cru_reset + (tx_bank * 4));
-		writel((BIT(rx_offset) << 16),
-		       cru_reset + (rx_bank * 4));
-		local_irq_restore(flags);
-	}
-}
-
 /*
  * Makes sure that both tx and rx are reset at the same time to sync lrck
  * when clk_trcm > 0.
  */
 static void rockchip_snd_xfer_sync_reset(struct rk_i2s_tdm_dev *i2s_tdm)
 {
-	int tx_id, rx_id;
-	int tx_bank, rx_bank, tx_offset, rx_offset;
-
-	if (!i2s_tdm->cru_base || !i2s_tdm->soc_data)
-		return;
-
-	tx_id = i2s_tdm->tx_reset_id;
-	rx_id = i2s_tdm->rx_reset_id;
-	if (tx_id < 0 || rx_id < 0)
-		return;
-
-	tx_bank = tx_id / 16;
-	tx_offset = tx_id % 16;
-	rx_bank = rx_id / 16;
-	rx_offset = rx_id % 16;
-	dev_dbg(i2s_tdm->dev,
-		"tx_bank: %d, rx_bank: %d, tx_offset: %d, rx_offset: %d\n",
-		tx_bank, rx_bank, tx_offset, rx_offset);
-
-	rockchip_snd_xfer_reset_assert(i2s_tdm, tx_bank, tx_offset,
-				       rx_bank, rx_offset);
+	/* This is technically race-y.
+	 *
+	 * In an ideal world, we could atomically assert both resets at the
+	 * same time, through an atomic bulk reset API. This API however does
+	 * not exist, so what the downstream vendor code used to do was
+	 * implement half a reset controller here and require the CRU to be
+	 * passed to the driver as a device tree node. Violating abstractions
+	 * like that is bad, especially when it influences something like the
+	 * bindings which are supposed to describe the hardware, not whatever
+	 * workarounds the driver needs, so it was dropped.
+	 *
+	 * In practice, asserting the resets one by one appears to work just
+	 * fine for playback. During duplex (playback + capture) operation,
+	 * this might become an issue, but that should be solved by the
+	 * implementation of the aforementioned API, not by shoving a reset
+	 * controller into an audio driver.
+	 */
 
+	reset_control_assert(i2s_tdm->tx_reset);
+	reset_control_assert(i2s_tdm->rx_reset);
 	udelay(10);
-
-	rockchip_snd_xfer_reset_deassert(i2s_tdm, tx_bank, tx_offset,
-					 rx_bank, rx_offset);
+	reset_control_deassert(i2s_tdm->tx_reset);
+	reset_control_deassert(i2s_tdm->rx_reset);
 	udelay(10);
 }
 
@@ -1361,24 +1310,6 @@ static const struct of_device_id rockchip_i2s_tdm_match[] = {
 	{},
 };
 
-static int of_i2s_resetid_get(struct device_node *node,
-			      const char *id)
-{
-	struct of_phandle_args args;
-	int index = 0;
-	int ret;
-
-	if (id)
-		index = of_property_match_string(node,
-						 "reset-names", id);
-	ret = of_parse_phandle_with_args(node, "resets", "#reset-cells",
-					 index, &args);
-	if (ret)
-		return ret;
-
-	return args.args[0];
-}
-
 static struct snd_soc_dai_driver i2s_tdm_dai = {
 	.probe = rockchip_i2s_tdm_dai_probe,
 	.playback = {
@@ -1591,7 +1522,6 @@ static int rockchip_i2s_tdm_rx_path_prepare(struct rk_i2s_tdm_dev *i2s_tdm,
 static int rockchip_i2s_tdm_probe(struct platform_device *pdev)
 {
 	struct device_node *node = pdev->dev.of_node;
-	struct device_node *cru_node;
 	const struct of_device_id *of_id;
 	struct rk_i2s_tdm_dev *i2s_tdm;
 	struct resource *res;
@@ -1633,20 +1563,6 @@ static int rockchip_i2s_tdm_probe(struct platform_device *pdev)
 		return dev_err_probe(i2s_tdm->dev, PTR_ERR(i2s_tdm->grf),
 				     "Error in rockchip,grf\n");
 
-	if (i2s_tdm->clk_trcm != TRCM_TXRX) {
-		cru_node = of_parse_phandle(node, "rockchip,cru", 0);
-		i2s_tdm->cru_base = of_iomap(cru_node, 0);
-		of_node_put(cru_node);
-		if (!i2s_tdm->cru_base) {
-			dev_err(i2s_tdm->dev,
-				"Missing or unsupported rockchip,cru node\n");
-			return -ENOENT;
-		}
-
-		i2s_tdm->tx_reset_id = of_i2s_resetid_get(node, "tx-m");
-		i2s_tdm->rx_reset_id = of_i2s_resetid_get(node, "rx-m");
-	}
-
 	i2s_tdm->tx_reset = devm_reset_control_get_optional_exclusive(&pdev->dev,
 								      "tx-m");
 	if (IS_ERR(i2s_tdm->tx_reset)) {