linux-kernel - Re: [RFC PATCH] tty: serial: msm_serial: Don't reset uart on set

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Message-ID: <5761FCC5.3010709@codeaurora.org>
Date:	Wed, 15 Jun 2016 18:11:33 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Bjorn Andersson <bjorn.andersson@...aro.org>,
	Andy Gross <andy.gross@...aro.org>,
	David Brown <david.brown@...aro.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	"open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@...r.kernel.org>,
	"open list:ARM/QUALCOMM SUPPORT" <linux-soc@...r.kernel.org>,
	"open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] tty: serial: msm_serial: Don't reset uart on
 set_termios

On 06/13/2016 12:02 PM, Bjorn Andersson wrote:
> Upon opening the tty, uart_open() ends up calling msm_set_baud_rate()
> which resets the uart block. If this happens as we're coming out of
> msm_console_write() a full fifo worth of console output will be
> discarded.
>
> Cc: Stephen Boyd <sboyd@...eaurora.org>
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> ---
>
> As reported here:
> https://bugs.96boards.org/show_bug.cgi?id=378

Urgh. As mentioned in commit a12f1b406f2d (tty: serial: msm: Reset
uartdm after baud rate change, 2014-10-29) we actually need to reset the
hardware sometimes. Perhaps as discussed over IRC we need to take a
different approach here and only reset the hardware if the baud actually
changes? One way to test this would be to try running a getty on the
console and see if input still works.

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