Messages in this thread | | | Date | Sat, 07 Feb 2015 16:19:37 +0100 | From | Noralf Trønnes <> | Subject | Re: [PATCH 2/8] fbdev: ssd1307fb: Unify init code and make controller configurable from device tree |
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Hi,
Den 07.02.2015 15:59, skrev Thomas Niederprüm: > Am Sat, 7 Feb 2015 11:42:25 +0100 > schrieb Maxime Ripard <maxime.ripard@free-electrons.com>: > >> Hi, >> >> On Fri, Feb 06, 2015 at 11:28:08PM +0100, niederp@physik.uni-kl.de >> wrote: >>> From: Thomas Niederprüm <niederp@physik.uni-kl.de> >>> >>> This patches unifies the init code for the ssd130X chips and >>> adds device tree bindings to describe the hardware configuration >>> of the used controller. This gets rid of the magic bit values >>> used in the init code so far. >>> >>> Signed-off-by: Thomas Niederprüm <niederp@physik.uni-kl.de> >>> --- >>> .../devicetree/bindings/video/ssd1307fb.txt | 11 + >>> drivers/video/fbdev/ssd1307fb.c | 243 >>> ++++++++++++++------- 2 files changed, 174 insertions(+), 80 >>> deletions(-) >>> >>> diff --git a/Documentation/devicetree/bindings/video/ssd1307fb.txt >>> b/Documentation/devicetree/bindings/video/ssd1307fb.txt index >>> 7a12542..1230f68 100644 --- >>> a/Documentation/devicetree/bindings/video/ssd1307fb.txt +++ >>> b/Documentation/devicetree/bindings/video/ssd1307fb.txt @@ -15,6 >>> +15,17 @@ Required properties: >>> Optional properties: >>> - reset-active-low: Is the reset gpio is active on physical low? >>> + - solomon,segment-remap: Invert the order of data column to >>> segment mapping >>> + - solomon,offset: Map the display start line to one of COM0 - >>> COM63 >>> + - solomon,contrast: Set initial contrast of the display >>> + - solomon,prechargep1: Set the duration of the precharge period >>> phase1 >>> + - solomon,prechargep2: Set the duration of the precharge period >>> phase2 >>> + - solomon,com-alt: Enable/disable alternate COM pin configuration >>> + - solomon,com-lrremap: Enable/disable left-right remap of COM >>> pins >>> + - solomon,com-invdir: Invert COM scan direction >>> + - solomon,vcomh: Set VCOMH regulator voltage >>> + - solomon,dclk-div: Set display clock divider >>> + - solomon,dclk-frq: Set display clock frequency >> I'm sorry, but this is the wrong approach, for at least two reasons: >> you broke all existing users of that driver, which is a clear no-go, > Unfortunately this is true. The problem is that the SSD130X controllers > allow for a very versatile wiring of the display to the controller. > It's over to the manufacturer of the OLED module (disp+controller) to > decide how it's actually wired and during device initialization the > driver has to take care to configure the SSD130X controller according > to that wiring. If the driver fails to do so you will end up having > your display showing garbage. Unfortunately the current sate of the > initialization code of the ssd1307fb driver is not very flexible in that > respect. Taking a look at the initialization code for the ssd1306 shows > that it was written with one very special display module in mind. Most > of the magic bit values set there are non-default values according to > the datasheet. The result is that the driver works with that one > particular display module but many other (differently wired) display > modules using a ssd1306 controller won't work without changing the > hardcoded magic bit values. > > My idea here was to set all configuration to the default values (as > given in the datasheet) unless it is overwritten by DT. Of course, > without a change in DT, this breaks the driver for all existing users. > The only alternative would be to set the current values as default. > Somehow this feels wrong to me as these values look arbitrary when you > don't know what exact display module they were set for. But if you > insist, I will change the default values. > >> and the DT itself should not contain any direct mapping of the >> registers. >> > I think I don't get what you mean here. Is it because I do no sanity > checks of the numbers set in DT? I was just looking for a way to hand > over the information about the wiring of display to the driver. How > would you propose to solve this?
I have the exact same challenge with the staging/fbtft drivers. I have asked about this on the DT list a couple of days ago, but no answer yet:
Can I do register initialization from Device Tree? http://www.spinics.net/lists/devicetree/msg68174.html
Regards, Noralf Trønnes
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