powerpc: Remove broken GregorianDay()

[Michael Ellerman]

On Tue, 2015-15-12 at 07:09:14 UTC, Daniel Axtens wrote:
> GregorianDay() is supposed to calculate the day of the week
> (tm->tm_wday) for a given day/month/year. In that calcuation it
> indexed into an array called MonthOffset using tm->tm_mon-1. However
> tm_mon is zero-based, not one-based, so this is off-by-one. It also
> means that every January, GregoiranDay() will access element -1 of
> the MonthOffset array.
> 
> It also doesn't appear to be a correct algorithm either: see in
> contrast kernel/time/timeconv.c's time_to_tm function.
> 
> It's been broken forever, which suggests no-one in userland uses
> this. It looks like no-one in the kernel uses tm->tm_wday either
> (see e.g. drivers/rtc/rtc-ds1305.c:319).
> 
> tm->tm_wday is conventionally set to -1 when not available in
> hardware so we can simply set it to -1 and drop the function.
> (There are over a dozen other drivers in drivers/rtc that do
> this.)
> 
> Found using UBSAN.
> 
> Cc: Andrey Ryabinin <aryabinin at virtuozzo.com>
> Cc: Andrew Morton <akpm at linux-foundation.org> # as an example of what UBSan finds.
> Cc: Alessandro Zummo <a.zummo at towertech.it>
> Cc: Alexandre Belloni <alexandre.belloni at free-electrons.com>
> Cc: rtc-linux at googlegroups.com
> Signed-off-by: Daniel Axtens <dja at axtens.net>
> Acked-by: Alexandre Belloni <alexandre.belloni at free-electrons.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/00b912b0c88e690b1662067497

cheers