linux-kernel - Re: [PATCH v2 0/4] fujitsu

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Date:   Mon, 6 Mar 2017 10:33:50 +0100
From:   Michał Kępień <kernel@...pniu.pl>
To:     Jonathan Woithe <jwoithe@...t42.net>
Cc:     Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/4] fujitsu_init() cleanup

> Hi Michael
> 
> Some quick feedback.
> 
> On Mon, Mar 06, 2017 at 03:31:04PM +1030, Jonathan Woithe wrote:
> > > > I can add that immediately after loading the driver the value returned by a
> > > > read of bl_power is 0.  As noted above, setting to 1 makes no difference to
> > > > the backlight, neither does returning it to 0.
> > > 
> > > Have you tried setting bl_power to 4?  Because that is the value of
> > > FB_BLANK_POWERDOWN, which is the value the patch is supposed to handle.
> > 
> > Oh no, I didn't try 4.  I should have.  I will try to squeeze in a test of
> > this tonight (time is short but the test won't take a lot of time).
> 
> With an unpatched 4.5 kernel, writing 4 (as opposed to 1, which I stupidly
> tried earlier) to bl_power caused the backlight to turn off.  Writing 0
> turned it back on again.
> 
> With patches 1-4/4 applied, writing 4 to bl_power did *NOT* turn the
> backlight off.
> 
> With patch 2 reverted, writing 4 to bl_power turned the backlight off. 
> Writing 0 to bl_power turned it back on again.
> 
> This means that patch 2/4 seems to prevent bl_power from operating as
> expected on the S7020 hardware.  Without this patch (but with all the others
> in place) bl_power works.
> 
> I am unlikely to have any more time to investigate this further tonight. 
> 
> In light of the above findings, what would you like to do?

Thanks for testing, good that we caught this before the patch series was
applied.  I think it is reasonable to skip applying this version of the
series as at least patch 2/4 is faulty and breaks a working feature.

Moving on, though, as I do not have access to Fujitsu hardware on which
this feature works, I was hoping you could help me verify whether my
assumptions were reasonable in the first place.  

I attached a crude patch to this message.  I would like to understand
how the underlying ACPI variables behave when the FEXT interface is
used, so please apply this patch on top of dvhart/testing (i.e. without
this series applied).  After compiling, please load the module with
debugging enabled, then test backlight control once again by writing 4
and then 0 to bl_power (this should work).  Then please send me all the
messages spit out by the driver into dmesg.  This should shed some light
on the matter.

Thanks!

-- 
Best regards,
Michał Kępień

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