serial: tegra: Correct delay after TX flush

For all tegra devices (up to t210), there is a hardware issue that
requires software to wait for 32 UART clock periods for the flush
to propagate otherwise TX data could be post. Add a helper function
to wait for N UART clock periods and update delay following FIFO
flush to be 32 UART clock cycles.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/serial-tegra.c b/drivers/tty/serial/serial-tegra.c
index 1d5ea39..9e08d3f 100644 (file)
--- a/drivers/tty/serial/serial-tegra.c
+++ b/drivers/tty/serial/serial-tegra.c
@@ -234,6 +234,22 @@ static void tegra_uart_break_ctl(struct uart_port *u, int break_ctl)
        tup->lcr_shadow = lcr;
 }
 
+/**
+ * tegra_uart_wait_cycle_time: Wait for N UART clock periods
+ *
+ * @tup:       Tegra serial port data structure.
+ * @cycles:    Number of clock periods to wait.
+ *
+ * Tegra UARTs are clocked at 16X the baud/bit rate and hence the UART
+ * clock speed is 16X the current baud rate.
+ */
+static void tegra_uart_wait_cycle_time(struct tegra_uart_port *tup,
+                                      unsigned int cycles)
+{
+       if (tup->current_baud)
+               udelay(DIV_ROUND_UP(cycles * 1000000, tup->current_baud * 16));
+}
+
 /* Wait for a symbol-time. */
 static void tegra_uart_wait_sym_time(struct tegra_uart_port *tup,
                unsigned int syms)
@@ -263,8 +279,12 @@ static void tegra_uart_fifo_reset(struct tegra_uart_port *tup, u8 fcr_bits)
        /* Dummy read to ensure the write is posted */
        tegra_uart_read(tup, UART_SCR);
 
-       /* Wait for the flush to propagate. */
-       tegra_uart_wait_sym_time(tup, 1);
+       /*
+        * For all tegra devices (up to t210), there is a hardware issue that
+        * requires software to wait for 32 UART clock periods for the flush
+        * to propagate, otherwise data could be lost.
+        */
+       tegra_uart_wait_cycle_time(tup, 32);
 }
 
 static int tegra_set_baudrate(struct tegra_uart_port *tup, unsigned int baud)