* Re: [Qemu-devel] [PATCH] PC Chipset: Improve serial divisor calculation
@ 2018-08-31 23:37 Guenter Roeck
2018-09-11 13:21 ` Paolo Bonzini
0 siblings, 1 reply; 3+ messages in thread
From: Guenter Roeck @ 2018-08-31 23:37 UTC (permalink / raw)
To: Calvin Lee; +Cc: Michael S. Tsirkin, Paolo Bonzini, qemu-devel
Hi,
On Fri, May 11, 2018 at 06:05:44PM -0600, Calvin Lee wrote:
> This fixes several problems I found in the UART serial implementation.
> Now all divisor values are allowed, while before divisor values of zero
> and below the base baud rate were rejected. All changes are in reference
> to http://www.sci.muni.cz/docs/pc/serport.txt
>
This patch is causing tracebacks in all Linux kernels running the PXA serial
driver. Here is an example:
[ 1.907584] ------------[ cut here ]------------
[ 1.907805] WARNING: CPU: 0 PID: 1 at drivers/tty/serial/pxa.c:544 serial_pxa_set_termios+0x254/0x268
[ 1.907865] Modules linked in:
[ 1.908130] CPU: 0 PID: 1 Comm: swapper Not tainted 4.9.125-rc1-00067-g7236e21 #1
[ 1.908155] Hardware name: Zipit Z2
[ 1.908783] [<c0011f54>] (unwind_backtrace) from [<c000e9ac>] (show_stack+0x20/0x24)
[ 1.908846] [<c000e9ac>] (show_stack) from [<c029aa80>] (dump_stack+0x20/0x28)
[ 1.908877] [<c029aa80>] (dump_stack) from [<c002befc>] (__warn+0xec/0x114)
[ 1.908905] [<c002befc>] (__warn) from [<c002bff4>] (warn_slowpath_null+0x30/0x38)
[ 1.908931] [<c002bff4>] (warn_slowpath_null) from [<c033eeb4>] (serial_pxa_set_termios+0x254/0x268)
[ 1.908958] [<c033eeb4>] (serial_pxa_set_termios) from [<c0339b00>] (uart_set_options+0xc8/0xf0)
[ 1.908987] [<c0339b00>] (uart_set_options) from [<c0712200>] (serial_pxa_console_setup+0xb4/0xc4)
...
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.
Guenter
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] [PATCH] PC Chipset: Improve serial divisor calculation
2018-08-31 23:37 [Qemu-devel] [PATCH] PC Chipset: Improve serial divisor calculation Guenter Roeck
@ 2018-09-11 13:21 ` Paolo Bonzini
2018-09-11 21:59 ` Guenter Roeck
0 siblings, 1 reply; 3+ messages in thread
From: Paolo Bonzini @ 2018-09-11 13:21 UTC (permalink / raw)
To: Guenter Roeck, Calvin Lee; +Cc: Michael S. Tsirkin, qemu-devel
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [Qemu-devel] [PATCH] PC Chipset: Improve serial divisor calculation
2018-09-11 13:21 ` Paolo Bonzini
@ 2018-09-11 21:59 ` Guenter Roeck
0 siblings, 0 replies; 3+ messages in thread
From: Guenter Roeck @ 2018-09-11 21:59 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: Calvin Lee, Michael S. Tsirkin, qemu-devel
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 <linux@roeck-us.net>
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
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2018-09-11 22:12 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2018-08-31 23:37 [Qemu-devel] [PATCH] PC Chipset: Improve serial divisor calculation Guenter Roeck
2018-09-11 13:21 ` Paolo Bonzini
2018-09-11 21:59 ` Guenter Roeck
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