Re: Patch "pwm: rockchip: Round period/duty down on apply, up on get" has been added to the 6.16-stable tree

[Greg KH <gregkh@linuxfoundation.org>]

On Sat, Aug 09, 2025 at 11:45:23AM +0200, Uwe Kleine-König wrote:
> Hello Sasha,
> 
> On Fri, Aug 08, 2025 at 06:30:33PM -0400, Sasha Levin wrote:
> > This is a note to let you know that I've just added the patch titled
> > 
> >     pwm: rockchip: Round period/duty down on apply, up on get
> > 
> > to the 6.16-stable tree which can be found at:
> >     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> > 
> > The filename of the patch is:
> >      pwm-rockchip-round-period-duty-down-on-apply-up-on-g.patch
> > and it can be found in the queue-6.16 subdirectory.
> > 
> > If you, or anyone else, feels it should not be added to the stable tree,
> > please let <stable@vger.kernel.org> know about it.
> > 
> > 
> > 
> > commit 51144efa3159cd95ab37e786c982822a060d7d1a
> > Author: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> > Date:   Mon Jun 16 17:14:17 2025 +0200
> > 
> >     pwm: rockchip: Round period/duty down on apply, up on get
> >     
> >     [ Upstream commit 0b4d1abe5ca568c5b7f667345ec2b5ad0fb2e54b ]
> >     
> >     With CONFIG_PWM_DEBUG=y, the rockchip PWM driver produces warnings like
> >     this:
> >     
> >       rockchip-pwm fd8b0010.pwm: .apply is supposed to round down
> >       duty_cycle (requested: 23529/50000, applied: 23542/50000)
> >     
> >     This is because the driver chooses ROUND_CLOSEST for purported
> >     idempotency reasons. However, it's possible to keep idempotency while
> >     always rounding down in .apply().
> >     
> >     Do this by making .get_state() always round up, and making .apply()
> >     always round down. This is done with u64 maths, and setting both period
> >     and duty to U32_MAX (the biggest the hardware can support) if they would
> >     exceed their 32 bits confines.
> >     
> >     Fixes: 12f9ce4a5198 ("pwm: rockchip: Fix period and duty cycle approximation")
> >     Fixes: 1ebb74cf3537 ("pwm: rockchip: Add support for hardware readout")
> >     Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
> >     Link: https://lore.kernel.org/r/20250616-rockchip-pwm-rounding-fix-v2-1-a9c65acad7b6@collabora.com
> >     Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>
> >     Signed-off-by: Sasha Levin <sashal@kernel.org>
> 
> while the new code makes the driver match the PWM rules now, I'd be
> conservative and not backport that patch because while I consider it a
> (very minor) fix that's a change in behaviour and maybe people depend on
> that old behaviour. So let's not break our user's workflows and reserve
> that for a major release. Please drop this patch from your queue.

Now dropped, but note, any behavior change is ok for ANY kernel version
as we guarantee they all work the same :)

So good luck with your users in the 6.17 release...

thanks

greg k-h