linux-kernel - Re: [PATCH 1/4] msm_serial: Fix NUL byte output on UARTDM

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Message-ID: <20130724202944.GB10926@codeaurora.org>
Date:	Wed, 24 Jul 2013 13:29:44 -0700
From:	David Brown <davidb@...eaurora.org>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH 1/4] msm_serial: Fix NUL byte output on UARTDM

On Wed, Jul 24, 2013 at 11:37:28AM -0700, Stephen Boyd wrote:
>UARTDM serial devices require us to wait for the entire TX fifo
>to drain before we can change the contents of the NCF_TX
>register. Furthermore, if we write any characters to the TX fifo
>within the same clock cycle of changing the NCF_TX register the
>NCF_TX register won't latch properly.
>
>To fix these issues we should read back the NCF_TX register to
>delay any TX fifo accesses by a clock cycle and we should wait
>for the TX fifo to drain (instead of just waiting for the fifo to
>be ready to receive more characters). Failure to do so leads to
>random NUL bytes interspersed in the output.
>
>Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
>---
> drivers/tty/serial/msm_serial.c | 14 +++++++++-----
> drivers/tty/serial/msm_serial.h |  1 +
> 2 files changed, 10 insertions(+), 5 deletions(-)

Acked-by: David Brown <davidb@...eaurora.org>

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