Re: [PATCH 1/3] [v2] powerpc: mac: fix rtc read/write functions

From: Michael Ellerman <mpe@ellerman.id.au>
To: Arnd Bergmann <arnd@arndb.de>, Paul Mackerras <paulus@samba.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Joshua Thompson <funaho@jurai.org>
Cc: Mathieu Malaterre <malat@debian.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Greg Ungerer <gerg@linux-m68k.org>,
	linux-m68k@lists.linux-m68k.org, linuxppc-dev@lists.ozlabs.org,
	linux-kernel@vger.kernel.org, y2038@lists.linaro.org,
	Meelis Roos <mroos@linux.ee>,
	Andreas Schwab <schwab@linux-m68k.org>,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH 1/3] [v2] powerpc: mac: fix rtc read/write functions
Date: Wed, 27 Jun 2018 14:32:17 +1000	[thread overview]
Message-ID: <87y3f06e9a.fsf@concordia.ellerman.id.au> (raw)
In-Reply-To: <20180619140229.3615110-1-arnd@arndb.de>

Arnd Bergmann <arnd@arndb.de> writes:

> As Mathieu pointed out, my conversion to time64_t was incorrect and resulted
> in negative times to be read from the RTC. The problem is that during the
> conversion from a byte array to a time64_t, the 'unsigned char' variable
> holding the top byte gets turned into a negative signed 32-bit integer
> before being assigned to the 64-bit variable for any times after 1972.
>
> This changes the logic to cast to an unsigned 32-bit number first for
> the Macintosh time and then convert that to the Unix time, which then gives
> us a time in the documented 1904..2040 year range. I decided not to use
> the longer 1970..2106 range that other drivers use, for consistency with
> the literal interpretation of the register, but that could be easily
> changed if we decide we want to support any Mac after 2040.
>
> Just to be on the safe side, I'm also adding a WARN_ON that will trigger
> if either the year 2040 has come and is observed by this driver, or we
> run into an RTC that got set back to a pre-1970 date for some reason
> (the two are indistinguishable).
>
> For the RTC write functions, Andreas found another problem: both
> pmu_request() and cuda_request() are varargs functions, so changing
> the type of the arguments passed into them from 32 bit to 64 bit
> breaks the API for the set_rtc_time functions. This changes it
> back to 32 bits.
>
> The same code exists in arch/m68k/ and is patched in an identical way now
> in a separate patch.
>
> Fixes: 5bfd643583b2 ("powerpc: use time64_t in read_persistent_clock")
> Reported-by: Mathieu Malaterre <malat@debian.org>
> Reported-by: Andreas Schwab <schwab@linux-m68k.org>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  arch/powerpc/platforms/powermac/time.c | 29 ++++++++++++++++++++---------
>  1 file changed, 20 insertions(+), 9 deletions(-)

So I think I can take this patch in isolation via the powerpc tree as a
fix for 4.18.

I'll leave the other two alone.

cheers