Re: [Qemu-devel] [PATCH] PC Chipset: Improve serial divisor calculation

[Paolo Bonzini <pbonzini@redhat.com>]

On 01/09/2018 01:37, Guenter Roeck wrote:
> The patch results in an unexpected DLL register value. Here is the
> surrounding code from drivers/tty/serial/pxa.c:
> 
> 	serial_out(up, UART_DLL, quot & 0xff);		/* LS of divisor */
> 
> 	/*
> 	 * work around Errata #75 according to Intel(R) PXA27x
> 	 * Processor Family Specification Update (Nov 2005)
> 	 */
> 	dll = serial_in(up, UART_DLL);
> 	WARN_ON(dll != (quot & 0xff));	// <-- warning
> 
> Reverting the patch fixes the problem.

I think it's a typo.  Can you try this:

diff --git a/hw/char/serial.c b/hw/char/serial.c
index 251f40fdac..02463e3388 100644
--- a/hw/char/serial.c
+++ b/hw/char/serial.c
@@ -345,9 +345,9 @@ static void serial_ioport_write(void *opaque, hwaddr addr, uint64_t val,
     default:
     case 0:
         if (s->lcr & UART_LCR_DLAB) {
-            if (size == 2) {
+            if (size == 1) {
                 s->divider = (s->divider & 0xff00) | val;
-            } else if (size == 4) {
+            } else {
                 s->divider = val;
             }
             serial_update_parameters(s);

Thanks,

Paolo