serial: tegra: check for FIFO mode enabled status

Chips prior to Tegra186 needed delay of 3 UART clock cycles to avoid
data loss. This issue is fixed in Tegra186 and a new flag is added to
check if FIFO mode is enabled. chip data updated to check if this flag
is available for a chip. Tegra186 has new compatible to enable this
flag.

Signed-off-by: Shardar Shariff Md <smohammed@nvidia.com>
Signed-off-by: Krishna Yarlagadda <kyarlagadda@nvidia.com>
Link: https://lore.kernel.org/r/1567572187-29820-7-git-send-email-kyarlagadda@nvidia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial-tegra.c

@@ -72,6 +72,8 @@
 #define TEGRA_TX_PIO				1
 #define TEGRA_TX_DMA				2
 
+#define TEGRA_UART_FCR_IIR_FIFO_EN		0x40
+
 /**
  * tegra_uart_chip_data: SOC specific data.
  *
@@ -84,6 +86,7 @@ struct tegra_uart_chip_data {
 	bool	tx_fifo_full_status;
 	bool	allow_txfifo_reset_fifo_mode;
 	bool	support_clk_src_div;
+	bool	fifo_mode_enable_status;
 };
 
 struct tegra_uart_port {
@@ -263,6 +266,21 @@ static void tegra_uart_wait_sym_time(struct tegra_uart_port *tup,
 			tup->current_baud));
 }
 
+static int tegra_uart_wait_fifo_mode_enabled(struct tegra_uart_port *tup)
+{
+	unsigned long iir;
+	unsigned int tmout = 100;
+
+	do {
+		iir = tegra_uart_read(tup, UART_IIR);
+		if (iir & TEGRA_UART_FCR_IIR_FIFO_EN)
+			return 0;
+		udelay(1);
+	} while (--tmout);
+
+	return -ETIMEDOUT;
+}
+
 static void tegra_uart_fifo_reset(struct tegra_uart_port *tup, u8 fcr_bits)
 {
 	unsigned long fcr = tup->fcr_shadow;
@@ -282,6 +300,8 @@ static void tegra_uart_fifo_reset(struct tegra_uart_port *tup, u8 fcr_bits)
 		tegra_uart_write(tup, fcr, UART_FCR);
 		fcr |= UART_FCR_ENABLE_FIFO;
 		tegra_uart_write(tup, fcr, UART_FCR);
+		if (tup->cdata->fifo_mode_enable_status)
+			tegra_uart_wait_fifo_mode_enabled(tup);
 	}
 
 	/* Dummy read to ensure the write is posted */
@@ -917,12 +937,20 @@ static int tegra_uart_hw_init(struct tegra_uart_port *tup)
 	/* Dummy read to ensure the write is posted */
 	tegra_uart_read(tup, UART_SCR);
 
-	/*
-	 * For all tegra devices (up to t210), there is a hardware issue that
-	 * requires software to wait for 3 UART clock periods after enabling
-	 * the TX fifo, otherwise data could be lost.
-	 */
-	tegra_uart_wait_cycle_time(tup, 3);
+	if (tup->cdata->fifo_mode_enable_status) {
+		ret = tegra_uart_wait_fifo_mode_enabled(tup);
+		dev_err(tup->uport.dev, "FIFO mode not enabled\n");
+		if (ret < 0)
+			return ret;
+	} else {
+		/*
+		 * For all tegra devices (up to t210), there is a hardware
+		 * issue that requires software to wait for 3 UART clock
+		 * periods after enabling the TX fifo, otherwise data could
+		 * be lost.
+		 */
+		tegra_uart_wait_cycle_time(tup, 3);
+	}
 
 	/*
 	 * Initialize the UART with default configuration
@@ -1293,12 +1321,21 @@ static struct tegra_uart_chip_data tegra20_uart_chip_data = {
 	.tx_fifo_full_status		= false,
 	.allow_txfifo_reset_fifo_mode	= true,
 	.support_clk_src_div		= false,
+	.fifo_mode_enable_status	= false,
 };
 
 static struct tegra_uart_chip_data tegra30_uart_chip_data = {
 	.tx_fifo_full_status		= true,
 	.allow_txfifo_reset_fifo_mode	= false,
 	.support_clk_src_div		= true,
+	.fifo_mode_enable_status	= false,
+};
+
+static struct tegra_uart_chip_data tegra186_uart_chip_data = {
+	.tx_fifo_full_status		= true,
+	.allow_txfifo_reset_fifo_mode	= false,
+	.support_clk_src_div		= true,
+	.fifo_mode_enable_status	= true,
 };
 
 static const struct of_device_id tegra_uart_of_match[] = {
@@ -1308,6 +1345,9 @@ static const struct of_device_id tegra_uart_of_match[] = {
 	}, {
 		.compatible	= "nvidia,tegra20-hsuart",
 		.data		= &tegra20_uart_chip_data,
+	}, {
+		.compatible     = "nvidia,tegra186-hsuart",
+		.data		= &tegra186_uart_chip_data,
 	}, {
 	},
 };