i2c: tegra: Use internal reset when reset property is not available

JIRA: https://issues.redhat.com/browse/RHEL-113177

commit 635bf3c
Author: Akhil R <akhilrajeev@nvidia.com>
Date: Thu, 10 Jul 2025 18:42:05 +0530

    For controllers that has an internal software reset, make the reset
    property optional. This provides and option to use I2C in systems
    that choose to restrict reset control from Linux or not to implement
    the ACPI _RST method.

    Internal reset was not required when the reset control was mandatory.
    But on platforms where the resets are outside the control of Linux,
    this had to be implemented by just returning success from BPMP or with
    an empty _RST method in the ACPI table, basically ignoring the reset.

    While the internal reset is not identical to the hard reset of the
    controller, this will reset all the internal state of the controller
    including FIFOs. This may slightly alter the behaviour in systems
    which were ignoring the reset but it should not cause any functional
    difference since all the required I2C registers are configured after
    this reset, just as in boot. Considering that this sequence is hit
    during the boot or during the I2C recovery path from an error, the
    internal reset provides a better alternative than just ignoring the
    reset.

    Signed-off-by: Akhil R <akhilrajeev@nvidia.com>
    Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
    Link: https://lore.kernel.org/r/20250710131206.2316-3-akhilrajeev@nvidia.com

Signed-off-by: Charles Mirabile <cmirabil@redhat.com>

Author: Charles Mirabile

drivers/i2c/busses/i2c-tegra.c

@@ -134,6 +134,8 @@
 #define I2C_MST_FIFO_STATUS_TX			GENMASK(23, 16)
 #define I2C_MST_FIFO_STATUS_RX			GENMASK(7, 0)
 
+#define I2C_MASTER_RESET_CNTRL			0x0a8
+
 /* configuration load timeout in microseconds */
 #define I2C_CONFIG_LOAD_TIMEOUT			1000000
 
@@ -184,6 +186,9 @@ enum msg_end_type {
  * @has_mst_fifo: The I2C controller contains the new MST FIFO interface that
  *		provides additional features and allows for longer messages to
  *		be transferred in one go.
+ * @has_mst_reset: The I2C controller contains MASTER_RESET_CTRL register which
+ *		provides an alternative to controller reset when configured as
+ *		I2C master
  * @quirks: I2C adapter quirks for limiting write/read transfer size and not
  *		allowing 0 length transfers.
  * @supports_bus_clear: Bus Clear support to recover from bus hang during
@@ -213,6 +218,7 @@ struct tegra_i2c_hw_feature {
 	bool has_multi_master_mode;
 	bool has_slcg_override_reg;
 	bool has_mst_fifo;
+	bool has_mst_reset;
 	const struct i2c_adapter_quirks *quirks;
 	bool supports_bus_clear;
 	bool has_apb_dma;
@@ -604,12 +610,42 @@ static int tegra_i2c_wait_for_config_load(struct tegra_i2c_dev *i2c_dev)
 	return 0;
 }
 
+static int tegra_i2c_master_reset(struct tegra_i2c_dev *i2c_dev)
+{
+	if (!i2c_dev->hw->has_mst_reset)
+		return -EOPNOTSUPP;
+
+	/*
+	 * Writing 1 to I2C_MASTER_RESET_CNTRL will reset all internal state of
+	 * Master logic including FIFOs. Clear this bit to 0 for normal operation.
+	 * SW needs to wait for 2us after assertion and de-assertion of this soft
+	 * reset.
+	 */
+	i2c_writel(i2c_dev, 0x1, I2C_MASTER_RESET_CNTRL);
+	fsleep(2);
+
+	i2c_writel(i2c_dev, 0x0, I2C_MASTER_RESET_CNTRL);
+	fsleep(2);
+
+	return 0;
+}
+
 static int tegra_i2c_init(struct tegra_i2c_dev *i2c_dev)
 {
 	u32 val, clk_divisor, clk_multiplier, tsu_thd, tlow, thigh, non_hs_mode;
 	struct i2c_timings *t = &i2c_dev->timings;
 	int err;
 
+	/*
+	 * Reset the controller before initializing it.
+	 * In case if device_reset() returns -ENOENT, i.e. when the reset is
+	 * not available, the internal software reset will be used if it is
+	 * supported by the controller.
+	 */
+	err = device_reset(i2c_dev->dev);
+	if (err == -ENOENT)
+		err = tegra_i2c_master_reset(i2c_dev);
+
 	/*
 	 * The reset shouldn't ever fail in practice. The failure will be a
 	 * sign of a severe problem that needs to be resolved. Still we don't
@@ -618,7 +654,6 @@ static int tegra_i2c_init(struct tegra_i2c_dev *i2c_dev)
 	 * emit a noisy warning on error, which won't stay unnoticed and
 	 * won't hose machine entirely.
 	 */
-	err = device_reset(i2c_dev->dev);
 	WARN_ON_ONCE(err);
 
 	if (IS_DVC(i2c_dev))
@@ -1469,6 +1504,7 @@ static const struct tegra_i2c_hw_feature tegra20_i2c_hw = {
 	.has_multi_master_mode = false,
 	.has_slcg_override_reg = false,
 	.has_mst_fifo = false,
+	.has_mst_reset = false,
 	.quirks = &tegra_i2c_quirks,
 	.supports_bus_clear = false,
 	.has_apb_dma = true,
@@ -1493,6 +1529,7 @@ static const struct tegra_i2c_hw_feature tegra30_i2c_hw = {
 	.has_multi_master_mode = false,
 	.has_slcg_override_reg = false,
 	.has_mst_fifo = false,
+	.has_mst_reset = false,
 	.quirks = &tegra_i2c_quirks,
 	.supports_bus_clear = false,
 	.has_apb_dma = true,
@@ -1517,6 +1554,7 @@ static const struct tegra_i2c_hw_feature tegra114_i2c_hw = {
 	.has_multi_master_mode = false,
 	.has_slcg_override_reg = false,
 	.has_mst_fifo = false,
+	.has_mst_reset = false,
 	.quirks = &tegra_i2c_quirks,
 	.supports_bus_clear = true,
 	.has_apb_dma = true,
@@ -1541,6 +1579,7 @@ static const struct tegra_i2c_hw_feature tegra124_i2c_hw = {
 	.has_multi_master_mode = false,
 	.has_slcg_override_reg = true,
 	.has_mst_fifo = false,
+	.has_mst_reset = false,
 	.quirks = &tegra_i2c_quirks,
 	.supports_bus_clear = true,
 	.has_apb_dma = true,
@@ -1565,6 +1604,7 @@ static const struct tegra_i2c_hw_feature tegra210_i2c_hw = {
 	.has_multi_master_mode = false,
 	.has_slcg_override_reg = true,
 	.has_mst_fifo = false,
+	.has_mst_reset = false,
 	.quirks = &tegra_i2c_quirks,
 	.supports_bus_clear = true,
 	.has_apb_dma = true,
@@ -1589,6 +1629,7 @@ static const struct tegra_i2c_hw_feature tegra186_i2c_hw = {
 	.has_multi_master_mode = false,
 	.has_slcg_override_reg = true,
 	.has_mst_fifo = false,
+	.has_mst_reset = false,
 	.quirks = &tegra_i2c_quirks,
 	.supports_bus_clear = true,
 	.has_apb_dma = false,
@@ -1613,6 +1654,7 @@ static const struct tegra_i2c_hw_feature tegra194_i2c_hw = {
 	.has_multi_master_mode = true,
 	.has_slcg_override_reg = true,
 	.has_mst_fifo = true,
+	.has_mst_reset = true,
 	.quirks = &tegra194_i2c_quirks,
 	.supports_bus_clear = true,
 	.has_apb_dma = false,