linux-kernel - Re: [PATCH RFC v2 04/11] tty: xuartps: Remove bogus comment and register write

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Message-ID: <20140308215748.4889aed8@alan.etchedpixels.co.uk>
Date:	Sat, 8 Mar 2014 21:57:48 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
Cc:	Russell King <linux@....linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, Arnd Bergmann <arnd@...db.de>,
	Michal Simek <michal.simek@...inx.com>,
	Peter Crosthwaite <peter.crosthwaite@...inx.com>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-serial@...r.kernel.org>
Subject: Re: [PATCH RFC v2 04/11] tty: xuartps: Remove bogus comment and
 register write

On Fri, 7 Mar 2014 15:08:00 -0800
Sören Brinkmann <soren.brinkmann@...inx.com> wrote:

> On Fri, 2014-03-07 at 09:28PM +0000, One Thousand Gnomes wrote:
> > On Fri,  7 Mar 2014 11:13:27 -0800
> > Soren Brinkmann <soren.brinkmann@...inx.com> wrote:
> > 
> > > Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
> > > ---
> > >  drivers/tty/serial/xilinx_uartps.c | 6 +-----
> > >  1 file changed, 1 insertion(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
> > > index a4bd6242e72d..a39c2d290902 100644
> > > --- a/drivers/tty/serial/xilinx_uartps.c
> > > +++ b/drivers/tty/serial/xilinx_uartps.c
> > > @@ -1082,11 +1082,7 @@ static void xuartps_console_write(struct console *co, const char *s,
> > >  
> > >  	xuartps_writel(ctrl, XUARTPS_CR_OFFSET);
> > >  
> > > -	/* restore interrupt state, it seems like there may be a h/w bug
> > > -	 * in that the interrupt enable register should not need to be
> > > -	 * written based on the data sheet
> > > -	 */
> > > -	xuartps_writel(~imr, XUARTPS_IDR_OFFSET);
> > > +	/* restore interrupt state */
> > 
> > It would be appropriate for the changelog at least to explain why the
> > note about the data sheet differing is going away !
> 
> I don't know why anybody ever thought things are broken. IMHO, the
> comment does not make any sense. Why would it not be required to write
> the enable register when you enable interrupts?
> I think someone read the data sheet wrong.

The comment reads very much like John Linn added it after trying to debug
a problem in real hardware. As such I think it warrants a bit more
calling out than a silent removal. That way if someone does find there is
a hardware bug (or some software race we don't understand) they will be
able to find the regression easily in the git log.

Alan
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