linux-kernel - Re: Linux 3.15: SPARC serial console regression

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Date:	Tue, 10 Jun 2014 21:24:38 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Aaro Koskinen <aaro.koskinen@....fi>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Seth Bollinger <sethb@...i.com>
Subject: Re: Linux 3.15: SPARC serial console regression

> From: Peter Hurley <peter@...leysoftware.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@...leysoftware.com>

Hi Peter.

Can you please take a look at sunzilog.c.
It looks like the same test is missing in sunzilog_start_tx():
        } else {
                struct circ_buf *xmit = &port->state->xmit;

                writeb(xmit->buf[xmit->tail], &channel->data);
                ZSDELAY();
                ZS_WSYNC(channel);

                xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
                port->icount.tx++;

                if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
                        uart_write_wakeup(&up->port);
        }


I did not review all drives - only a few sun drivers
and this was the only one that occured to me also
required this check.

I also noticed the typical pattern is:

    if (uart_circ_empty(xmit) || uart_tx_stopped(port))

Should you use this pattern also in sunsab.c?

	Sam
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