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SubjectRe: Linux 3.15: serial console regression
Hi,

On Mon, Jun 09, 2014 at 07:48:17PM -0400, Peter Hurley wrote:
> On 06/09/2014 04:59 PM, Aaro Koskinen wrote:> Hi,
> > While testing the final 3.15, I noticed the serial console (sunsab)
> > does not work anymore on Sun Ultra.
> >
> > It will tx fine the console output during the boot. But then I try
> > to type something e.g. at the login: prompt, it behaves oddly:
> > it re-transmits some old output, and then stalls for a few secs, usually
> > for each character. Typed characters are however received correctly.
> > But the console is impossible to use...
> >
> > I bisected this to:
> >
> > 717f3bbab3c7628736ef738fdbf3d9a28578c26c is the first bad commit
> > commit 717f3bbab3c7628736ef738fdbf3d9a28578c26c
> > Author: Seth Bollinger <sethb@digi.com>
> > Date: Tue Mar 25 12:55:37 2014 -0500
> >
> > serial_core: Fix conditional start_tx on ring buffer not empty
>
> [Let's try that again. This time without the mess]
>
> Thanks for the report Aaro.
>
> Looks like Seth's fix exposes some broken assumptions in the Sun
> serial drivers.

The same problem is present also on PowerPC G5 Xserve (pmac_zilog driver),
and the below type of fix works there too.

A.

> --- %< ---
> From: Peter Hurley <peter@hurleysoftware.com>
> Date: Mon, 9 Jun 2014 19:21:43 -0400
> Subject: [PATCH] serial: sunsab: Test for no tx data on tx restart
>
> Commit 717f3bbab3c7628736ef738fdbf3d9a28578c26c,
> 'serial_core: Fix conditional start_tx on ring buffer not empty'
> exposes an incorrect assumption in sunsab's start_tx method; the
> tx ring buffer can, in fact, be empty when restarting tx when
> performing flow control.
>
> Test for empty tx ring buffer when in sunsab's start_tx method.
>
> Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
> ---
> drivers/tty/serial/sunsab.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/tty/serial/sunsab.c b/drivers/tty/serial/sunsab.c
> index 5faa8e9..b99a4ea 100644
> --- a/drivers/tty/serial/sunsab.c
> +++ b/drivers/tty/serial/sunsab.c
> @@ -427,6 +427,9 @@ static void sunsab_start_tx(struct uart_port *port)
> struct circ_buf *xmit = &up->port.state->xmit;
> int i;
>
> + if (uart_circ_empty(xmit))
> + return;
> +
> up->interrupt_mask1 &= ~(SAB82532_IMR1_ALLS|SAB82532_IMR1_XPR);
> writeb(up->interrupt_mask1, &up->regs->w.imr1);
>
> --
> 2.0.0
>
> --
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