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


From: Guenter Roeck
Subject: Re: [Qemu-devel] [PATCH] PC Chipset: Improve serial divisor calculation
Date: Tue, 11 Sep 2018 14:59:30 -0700
User-agent: Mutt/1.5.24 (2015-08-30)

On Tue, Sep 11, 2018 at 03:21:34PM +0200, Paolo Bonzini wrote:
> 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:
> 

You are correct, the patch below fixes the problem.

Tested-by: Guenter Roeck <address@hidden>

Thanks!
Guenter

> 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



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