Hi,

Den 07.02.2015 15:59, skrev Thomas Niederprüm:

Am Sat, 7 Feb 2015 11:42:25 +0100
schrieb Maxime Ripard [off-list ref]:

quoted

Hi,

On Fri, Feb 06, 2015 at 11:28:08PM +0100, niederp@physik.uni-kl.de
wrote:

quoted

From: Thomas Niederprüm <redacted>

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 <redacted>
---
  .../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.

quoted

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