linux-kernel - Re: [PATCH 4.19 521/639] rtc: pcf2127: bugfix: read rtc disables watchdog

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Date:   Sun, 26 Jan 2020 14:19:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Bruno Thomsen <bruno.thomsen@...il.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 521/639] rtc: pcf2127: bugfix: read rtc disables
 watchdog

On Sun, Jan 26, 2020 at 11:26:35AM +0100, Pavel Machek wrote:
> On Fri 2020-01-24 10:31:31, Greg Kroah-Hartman wrote:
> > From: Bruno Thomsen <bruno.thomsen@...il.com>
> > 
> > [ Upstream commit 7f43020e3bdb63d65661ed377682702f8b34d3ea ]
> > 
> > The previous fix listed bulk read of registers as root cause of
> > accendential disabling of watchdog, since the watchdog counter
> > register (WD_VAL) was zeroed.
> > 
> > Fixes: 3769a375ab83 rtc: pcf2127: bulk read only date and time registers.
> > 
> > Tested with the same PCF2127 chip as Sean reveled root cause
> > of WD_VAL register value zeroing was caused by reading CTRL2
> > register which is one of the watchdog feature control registers.
> > 
> > So the solution is to not read the first two control registers
> > (CTRL1 and CTRL2) in pcf2127_rtc_read_time as they are not
> > needed anyway. Size of local buf variable is kept to allow
> > easy usage of register defines to improve readability of code.
> 
> Should the array be zeroed before or something? This way, one array
> contains both undefined values and valid data...
> 
> > Debug trace line was updated after CTRL1 and CTRL2 are no longer
> > read from the chip. Also replaced magic numbers in buf access
> > with register defines.
> 
> That part is not an improvement. Previously the code was formatted so
> that you could parse what is being printed.

Meta-comment: Making review comments on patches that are already in
Linus's tree, is fine, but making them here seems a bit odd.  Please
just go find the original patch and respond there, as there's not much
you can do here _way_ after the fact, as the change is already
committed.

thanks,

greg k-h