Date:   Mon, 6 Mar 2017 15:31:04 +1030
From:   Jonathan Woithe <jwoithe@...t42.net>
To:     Micha?? K??pie?? <kernel@...pniu.pl>
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

On Mon, Mar 06, 2017 at 05:49:05AM +0100, Micha?? K??pie?? wrote:
> > > With regard to patch 2/4 you wrote:
> > > > Jonathan, this *really* needs testing on relevant hardware.  After
> > > > applying this patch, you should be able to turn LCD backlight on and off
> > > > using /sys/class/backlight/fujitsu-laptop/bl_power.  Also, the value
> > > > returned by that attribute upon read should be in sync with actual
> > > > backlight state even right after loading the module (i.e. before writing
> > > > anything to bl_power).  Please let me know if any of the above is not
> > > > true and the module works correctly without this patch applied.
> > > 
> > > With patch 2/4 applied:
> > > 
> > >  * It is possible to read bl_power
> > > 
> > >  * It is possible to write a value to bl_power and read that value back
> > > 
> > >  * Writing values to bl_power does not appear to affect the LCD panel in 
> > >    any way.  That is, the backlight remains unchanged regardless of the 
> > >    value written.
> > > 
> > >  * Behaviour is the same both under X and from the terminal.
> > > 
> > > Backing out patch 2/4 but with all others still in place, resulted in no
> > > change in behaviour.  So while bl_power had no effect with patch 2/4 in
> > > place, it seems that patch 2/4 is *not* the cause of this.
> > > 
> > > I shall run some more bl_power tests and complete a review of the code later
> > > this weekend.
> > 
> > I have completed a review of the code in this patch series (patches 1-4 of
> > 4) and can find no obvious problems.  There do not appear to be any
> > regressions introduced by this patch series.  As noted, patch 2/4 does not
> > provide working backlight power control on an S7020 but it may well be that
> > this has never been functional on the S7020 (I do not make use of bl_power
> > myself).
> > 
> > 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).

> > A value of 0 would normally indicate that it's on I think,
> 
> Yes, I believe so too as 0 corresponds to FB_BLANK_UNBLANK.
> 
> > which means that the initial read of the
> > backlight power state does not appear to be working either.
> 
> So I assume you have some kind of external display connected and the LCD
> backlight is off, correct?  Just curious at this point.

No, I got myself horribly confused when I wrote that second bit (I'll blame
a lack of sleep).  Ignore it.  FYI all tests have been done without an
external monitor connected.

> > As for the
> > other behaviour, this does not change if patch 2/4 is omitted.
> 
> Commit 3a407086090b ("fujitsu-laptop: Add BL power, LED control and
> radio state information") which introduced backlight control mentions it
> was "tested on the S6420, P8010 & U810 platforms".  Not sure if
> backlight control was tested on all these models 

I vaguely recall that the person who contributed this commit did have access
to those three models, but I could be mistaken.

> and S7020 is not listed here,

I guess that's because the contributor didn't have an S7020 and therefore it
didn't appear in their commit message.  I can't recall whether I tested it
on an S7020 at the time; if I did perhaps I didn't see the point in
modifying the original commit message.  In retrospect that might have been
an error on my part.

> though I still find it puzzling that it did not work in the first
> place, i.e. without this series applied.  This patch emerged from
> reading the DSDT table of a S7020, so I would expect backlight control
> to at least work properly through the "officially exposed" interface,
> i.e. FEXT.

Let me try a value of 4 and see if that works.  As I said, I haven't ever
routinely used bl_power so at this stage I can't say for sure whether it's
worked or not.  Besides, I was stupidly using the wrong value when testing
it over the weekend (1 instead of 4) so this could all be a moot point.

> > Unfortunately I ran out of time over the weekend to cross check the
> > behaviour of bl_power on the S7020 with an unpatched kernel (as mentioned, I
> > don't utilise bl_power routinely myself and therefore can't recall whether
> > it has worked on my hardware in the past).  For completeness I will try to
> > look at this sometime this week.  However, given the patch content and the
> > observation that omitting patch 2/4 makes no difference to the S7020
> > behaviour I am satisfied that at least on S7020 this patch series does not
> > introduce any regressions and represents a worthwhile clean up of the
> > driver's code.
> 
> I would be happy to hear from someone for whom bl_power works as
> expected, though we really should not leave that backlight sync code
> where it currently is, so I am happy this is the conclusion you came to.

Indeed, the more testing the better.  I'll respond in a few hours with the
outcome of a test with "bl_power" set to 4.  Regardless of the outcome I
don't believe this issue should hold up the patch series for previously
stated reasons.

Regards
  jonathan

Powered by blists - more mailing lists