Re: [PATCH AUTOSEL 5.4 053/205] pwm: sun4i: Fix incorrect calculation of duty_cycle/period

[Uwe Kleine-König]

On Thu, Jan 16, 2020 at 11:40:28AM -0500, Sasha Levin wrote:
> From: Ondrej Jirman <megous@xxxxxxxxxx>
> 
> [ Upstream commit 50cc7e3e4f26e3bf5ed74a8d061195c4d2161b8b ]
> 
> Since 5.4-rc1, pwm_apply_state calls ->get_state after ->apply
> if available, and this revealed an issue with integer precision
> when calculating duty_cycle and period for the currently set
> state in ->get_state callback.
> 
> This issue manifested in broken backlight on several Allwinner
> based devices.
> 
> Previously this worked, because ->apply updated the passed state
> directly.
> 
> Fixes: deb9c462f4e53 ("pwm: sun4i: Don't update the state for the caller of pwm_apply_state")
> Signed-off-by: Ondrej Jirman <megous@xxxxxxxxxx>
> Acked-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> Signed-off-by: Thierry Reding <thierry.reding@xxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

Note that while the patch is still correct, the problem isn't that bad
any more since commit 01ccf903edd65f6421612321648fa5a7f4b7cb10 was
reverted.

So .get_state is only called once during boot where the breakage doesn't
hurt that much.

I let you decide if you still want to apply this patch.

Best regards
Uwe

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Pengutronix e.K.                           | Uwe Kleine-König            |
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