serial: qcom_geni_serial: Support kgdboc_earlycon

Implement the read() function in the early console driver.  With
recent kgdb patches this allows you to use kgdb to debug fairly early
into the system boot.

We only bother implementing this if polling is enabled since kgdb
can't be enabled without that.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20200507130644.v4.10.If2deff9679a62c1ce1b8f2558a8635dc837adf8c@changeid
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>

diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
index 6119090ce045d726e54015c989f11e19473bb492..6bace1c6bb09a95e67c01cd90c0358c1d8ca9848 100644 (file)
--- a/drivers/tty/serial/qcom_geni_serial.c
+++ b/drivers/tty/serial/qcom_geni_serial.c
@@ -1090,6 +1090,36 @@ static void qcom_geni_serial_earlycon_write(struct console *con,
        __qcom_geni_serial_console_write(&dev->port, s, n);
 }
 
+#ifdef CONFIG_CONSOLE_POLL
+static int qcom_geni_serial_earlycon_read(struct console *con,
+                                         char *s, unsigned int n)
+{
+       struct earlycon_device *dev = con->data;
+       struct uart_port *uport = &dev->port;
+       int num_read = 0;
+       int ch;
+
+       while (num_read < n) {
+               ch = qcom_geni_serial_get_char(uport);
+               if (ch == NO_POLL_CHAR)
+                       break;
+               s[num_read++] = ch;
+       }
+
+       return num_read;
+}
+
+static void __init qcom_geni_serial_enable_early_read(struct geni_se *se,
+                                                     struct console *con)
+{
+       geni_se_setup_s_cmd(se, UART_START_READ, 0);
+       con->read = qcom_geni_serial_earlycon_read;
+}
+#else
+static inline void qcom_geni_serial_enable_early_read(struct geni_se *se,
+                                                     struct console *con) { }
+#endif
+
 static int __init qcom_geni_serial_earlycon_setup(struct earlycon_device *dev,
                                                                const char *opt)
 {
@@ -1136,6 +1166,8 @@ static int __init qcom_geni_serial_earlycon_setup(struct earlycon_device *dev,
 
        dev->con->write = qcom_geni_serial_earlycon_write;
        dev->con->setup = NULL;
+       qcom_geni_serial_enable_early_read(&se, dev->con);
+
        return 0;
 }
 OF_EARLYCON_DECLARE(qcom_geni, "qcom,geni-debug-uart",