From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Pascal Roeleven <dev@pascalroeleven.nl>
Cc: linux-pwm@vger.kernel.org, linux-sunxi@googlegroups.com,
linux-kernel@vger.kernel.org, Maxime Ripard <mripard@kernel.org>,
Chen-Yu Tsai <wens@csie.org>,
Thierry Reding <thierry.reding@gmail.com>,
Philipp Zabel <p.zabel@pengutronix.de>,
linux-arm-kernel@lists.infradead.org
Subject: Re: pwm: sun4i: pwm-backlight not working since 5.6-rc1
Date: Thu, 12 Mar 2020 14:29:42 +0100 [thread overview]
Message-ID: <20200312132942.2kfspvmoc3mxkdx4@pengutronix.de> (raw)
In-Reply-To: <6185b5540ca082d887d7d13330c9d938@pascalroeleven.nl>
On Thu, Mar 12, 2020 at 01:22:13PM +0100, Pascal Roeleven wrote:
> Hi all,
>
> I am working on adding an old A10 device to mainline and noticed an issue
> when testing on 5.5.8 vs master.
>
> Since 5.6-rc1, I can't control the brightness of my LCD backlight anymore.
> The backlight stays on full brightness instead. I am controlling the
> brightness value via sysfs for testing.
>
> I am not sure if this is a general pwm-sun4i issue or if it is related to
> the backlight. However I narrowed it down to one commit for pwm-sun4i:
>
> fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5
>
> If I use pwm-sun4i.c from 5b090b430d750961305030232314b6acdb0102aa on
> master, the backlight works fine. Unfortunately, due to my lack of kernel
> experience, I can't see how the commit above broke it.
Hmm, I cannot see how fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5 breaks
this. Looking at the output of
git show -b fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5
(i.e. ignoring whitespace changes) I don't see how the behaviour you're
reporting can be explained.
Are you sure that fa4d81784681a26bcf7d2a43c6ac5cf991ef28f5 is the bad
commit?
Can you install a tool to inspect register values and check how the
affected registers change if you switch kernel versions and/or pwm
settings?
(e.g.
memtool md 0x1c20e00+0xc
)
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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next prev parent reply other threads:[~2020-03-12 13:29 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-12 12:22 pwm: sun4i: pwm-backlight not working since 5.6-rc1 Pascal Roeleven
2020-03-12 13:29 ` Uwe Kleine-König [this message]
2020-03-12 15:06 ` Pascal Roeleven
2020-03-16 7:26 ` Uwe Kleine-König
2020-03-17 17:32 ` Uwe Kleine-König
2020-03-17 17:52 ` Pascal Roeleven
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