linux-kernel - Re: [PATCH] serial: imx: fix cached UCR2 read on software reset

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Message-ID: <20180420060315.ob6eygfcibwq7f24@pengutronix.de>
Date:   Fri, 20 Apr 2018 08:03:15 +0200
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Stefan Agner <stefan@...er.ch>
Cc:     gregkh@...uxfoundation.org, jslaby@...e.com,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: imx: fix cached UCR2 read on software reset

Hello Stefan,

On Thu, Apr 19, 2018 at 11:37:23PM +0200, Stefan Agner wrote:
> On 16.04.2018 17:35, Stefan Agner wrote:
> > To reset the UART the SRST needs be cleared (low active). According
> > to the documentation the bit will remain active for 4 module clocks
> > until it is cleared (set to 1).
> > 
> > Hence the real register need to be read in case the cached register
> > indcates that the SRST bit is zero.
> > 
> > This bug lead to wrong baudrate because the baud rate register got
> > restored before reset completed in imx_flush_buffer.
> 
> Given that you reviewed my other patch rather quickly, you might have
> overlooked this one?

no I didn't, still the ping was justified. I didn't look into it at once
because I didn't feel like opening the refman.
 
> Since it is a regression, this should go into v4.17 still...

That's right,

Reviewed-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>

I wonder what is different on your side that made it break. I didn't see
any breakage and tested that on a handful of different machines.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |