serial: 8250_dw: Decouple DLF register check from UCV

Designware UART has an optional feature to enable Fractional Baud Rate
Divisor (DLF) through the FRACTIONAL_BAUD_DIVISOR_EN configuration
parameter, and it is not dependent on ADDITIONAL_FEATURES.

dw8250_setup_port() checks DLF to determine dlf_size only when UART
Component Version (UCV) is non-zero. As mentioned above DLF and UCV are
independent features. Move the logic corresponding to DLF size
calculation ahead of the UCV check to prevent early return. Otherwise,
dlf_size will be zero and driver will not be able to use the
controller's fractional baud rate divisor (DLF) feature.

Signed-off-by: Vamshi Gajjela <vamshigajjela@google.com>
Link: https://lore.kernel.org/r/20231126160420.2442330-1-vamshigajjela@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_dwlib.c b/drivers/tty/serial/8250/8250_dwlib.c
index 84843e204a5e80e872ab840e9069cc73a018d38d..136ad093c5b60623ee52dd906733412afbad7794 100644 (file)
--- a/drivers/tty/serial/8250/8250_dwlib.c
+++ b/drivers/tty/serial/8250/8250_dwlib.c
@@ -259,17 +259,6 @@ void dw8250_setup_port(struct uart_port *p)
        }
        up->capabilities |= UART_CAP_NOTEMT;
 
-       /*
-        * If the Component Version Register returns zero, we know that
-        * ADDITIONAL_FEATURES are not enabled. No need to go any further.
-        */
-       reg = dw8250_readl_ext(p, DW_UART_UCV);
-       if (!reg)
-               return;
-
-       dev_dbg(p->dev, "Designware UART version %c.%c%c\n",
-               (reg >> 24) & 0xff, (reg >> 16) & 0xff, (reg >> 8) & 0xff);
-
        /* Preserve value written by firmware or bootloader  */
        old_dlf = dw8250_readl_ext(p, DW_UART_DLF);
        dw8250_writel_ext(p, DW_UART_DLF, ~0U);
@@ -282,6 +271,17 @@ void dw8250_setup_port(struct uart_port *p)
                p->set_divisor = dw8250_set_divisor;
        }
 
+       /*
+        * If the Component Version Register returns zero, we know that
+        * ADDITIONAL_FEATURES are not enabled. No need to go any further.
+        */
+       reg = dw8250_readl_ext(p, DW_UART_UCV);
+       if (!reg)
+               return;
+
+       dev_dbg(p->dev, "Designware UART version %c.%c%c\n",
+               (reg >> 24) & 0xff, (reg >> 16) & 0xff, (reg >> 8) & 0xff);
+
        reg = dw8250_readl_ext(p, DW_UART_CPR);
        if (!reg) {
                reg = data->pdata->cpr_val;