serial: 8250_dw: Do not bailout on UCV read returning zero

Designware UART has optional feature FIFO_MODE to implement FIFO.
Encoding FIFO capabilities through Component Parameter Register CPR is
optional and it can be enabled using parameter UART_ADD_ENCODED_PARAMS.

Driver can exercise fifo capabilities by decoding CPR if implemented
or from cpr_val provided from the dw8250_platform_data otherwise.

dw8250_setup_port() checks for CPR or cpr_val to determine FIFO size
only when Component Version (UCV) is non-zero. Bailing out early on UCV
read returning zero will leave fifosize as zero and !UART_CAP_FIFO,
hence prevent early return and continue to process CPR or cpr_val for
the driver to utilize FIFO.

Non-zero UCV implies ADDITIONAL_FEATURES=1, preventing early return
will not be an overhead here.

Signed-off-by: Vamshi Gajjela <vamshigajjela@google.com>
Link: https://lore.kernel.org/r/20231231182951.877805-1-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 136ad093c5b60623ee52dd906733412afbad7794..3e33ddf7bc8007af3fc7a27ae6a8eda4f5499883 100644 (file)
--- a/drivers/tty/serial/8250/8250_dwlib.c
+++ b/drivers/tty/serial/8250/8250_dwlib.c
@@ -271,16 +271,10 @@ 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);
+       if (reg)
+               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) {