[ARM] 3407/1: lpd7x: documetation update

README on the ADC/Touchscreen Controller

========================================

The LH79524 and LH7A404 include a built-in Analog to Digital

controller (ADC) that is used to process input from a touchscreen.

The driver only implements a four-wire touch panel protocol.

The touchscreen driver is maintenance free except for the pen-down or

touch threshold.  Some resistive displays and board combinations may

require tuning of this threshold.  The driver exposes some of it's

internal state in the sys filesystem.  If the kernel is configured

with it, CONFIG_SYSFS, and sysfs is mounted at /sys, there will be a

directory

  /sys/devices/platform/adc-lh7.0

containing these files.

  -r--r--r--    1 root     root         4096 Jan  1 00:00 samples

  -rw-r--r--    1 root     root         4096 Jan  1 00:00 threshold

  -r--r--r--    1 root     root         4096 Jan  1 00:00 threshold_range

The threshold is the current touch threshold.  It defaults to 750 on

most targets.

  # cat threshold

 750

The threshold_range contains the range of valid values for the

threshold.  Values outside of this range will be silently ignored.

  # cat threshold_range

  0 1023

To change the threshold, write a value to the threshold file.

  # echo 500 > threshold

  # cat threshold

  500

The samples file contains the most recently sampled values from the

ADC.  There are 12.  Below are typical of the last sampled values when

the pen has been released.  The first two and last two samples are for

detecting whether or not the pen is down.  The third through sixth are

X coordinate samples.  The seventh through tenth are Y coordinate

samples.

  # cat samples

  1023 1023 0 0 0 0 530 529 530 529 1023 1023

To determine a reasonable threshold, press on the touch panel with an

appropriate stylus and read the values from samples.

  # cat samples

  1023 676 92 103 101 102 855 919 922 922 1023 679

The first and eleventh samples are discarded.  Thus, the important

values are the second and twelfth which are used to determine if the

pen is down.  When both are below the threshold, the driver registers

that the pen is down.  When either is above the threshold, it

registers then pen is up.

README on the LCD Panels

========================

Configuration options for several LCD panels, available from Logic PD,

are included in the kernel source.  This README will help you

understand the configuration data and give you some guidance for

adding support for other panels if you wish.

lcd-panels.h

------------

There is no way, at present, to detect which panel is attached to the

system at runtime.  Thus the kernel configuration is static.  The file

arch/arm/mach-ld7a40x/lcd-panels.h (or similar) defines all of the

panel specific parameters.

It should be possible for this data to be shared among several device

families.  The current layout may be insufficiently general, but it is

amenable to improvement.

PIXEL_CLOCK

-----------

The panel data sheets will give a range of acceptable pixel clocks.

The fundamental LCDCLK input frequency is divided down by a PCD

constant in field '.tim2'.  It may happen that it is impossible to set

the pixel clock within this range.  A clock which is too slow will

tend to flicker.  For the highest quality image, set the clock as high

as possible.

MARGINS

-------

These values may be difficult to glean from the panel data sheet.  In

the case of the Sharp panels, the upper margin is explicitly called

out as a specific number of lines from the top of the frame.  The

other values may not matter as much as the panels tend to

automatically center the image.

Sync Sense

----------

The sense of the hsync and vsync pulses may be called out in the data

sheet.  On one panel, the sense of these pulses determine the height

of the visible region on the panel.  Most of the Sharp panels use

negative sense sync pulses set by the TIM2_IHS and TIM2_IVS bits in

'.tim2'.

Pel Layout

----------

The Sharp color TFT panels are all configured for 16 bit direct color

modes.  The amba-lcd driver sets the pel mode to 565 for 5 bits of

each red and blue and 6 bits of green.