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@xxxxxxxxxx>
---
drivers/tty/serial/serial-tegra.c | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/serial/serial-tegra.c b/drivers/tty/serial/serial-tegra.c
index 1d5ea3964ee5..9e08d3f07509 100644
--- 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)
--
1.9.1
--
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