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[ARM] 3407/1: lpd7x: documetation update
Patch from Marc Singer
New documentation for the touchscreen controllers and LCD panels.
Signed-off-by: Marc Singer <elf@buici.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
authored by
Marc Singer
and committed by
Russell King
51cb21a9
d4adcffb
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Documentation/arm/Sharp-LH/ADC-LH7-Touchscreen
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Documentation/arm/Sharp-LH/ADC-LH7-Touchscreen
···
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README on the ADC/Touchscreen Controller
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========================================
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The LH79524 and LH7A404 include a built-in Analog to Digital
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controller (ADC) that is used to process input from a touchscreen.
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The driver only implements a four-wire touch panel protocol.
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The touchscreen driver is maintenance free except for the pen-down or
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touch threshold. Some resistive displays and board combinations may
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require tuning of this threshold. The driver exposes some of it's
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internal state in the sys filesystem. If the kernel is configured
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with it, CONFIG_SYSFS, and sysfs is mounted at /sys, there will be a
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directory
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/sys/devices/platform/adc-lh7.0
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containing these files.
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-r--r--r-- 1 root root 4096 Jan 1 00:00 samples
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-rw-r--r-- 1 root root 4096 Jan 1 00:00 threshold
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-r--r--r-- 1 root root 4096 Jan 1 00:00 threshold_range
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The threshold is the current touch threshold. It defaults to 750 on
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most targets.
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# cat threshold
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750
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The threshold_range contains the range of valid values for the
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threshold. Values outside of this range will be silently ignored.
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# cat threshold_range
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0 1023
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To change the threshold, write a value to the threshold file.
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# echo 500 > threshold
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# cat threshold
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500
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The samples file contains the most recently sampled values from the
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ADC. There are 12. Below are typical of the last sampled values when
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the pen has been released. The first two and last two samples are for
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detecting whether or not the pen is down. The third through sixth are
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X coordinate samples. The seventh through tenth are Y coordinate
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samples.
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# cat samples
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1023 1023 0 0 0 0 530 529 530 529 1023 1023
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To determine a reasonable threshold, press on the touch panel with an
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appropriate stylus and read the values from samples.
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# cat samples
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1023 676 92 103 101 102 855 919 922 922 1023 679
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The first and eleventh samples are discarded. Thus, the important
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values are the second and twelfth which are used to determine if the
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pen is down. When both are below the threshold, the driver registers
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that the pen is down. When either is above the threshold, it
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registers then pen is up.
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Documentation/arm/Sharp-LH/LCDPanels
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Documentation/arm/Sharp-LH/LCDPanels
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README on the LCD Panels
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========================
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Configuration options for several LCD panels, available from Logic PD,
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are included in the kernel source. This README will help you
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understand the configuration data and give you some guidance for
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adding support for other panels if you wish.
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lcd-panels.h
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------------
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There is no way, at present, to detect which panel is attached to the
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system at runtime. Thus the kernel configuration is static. The file
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arch/arm/mach-ld7a40x/lcd-panels.h (or similar) defines all of the
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panel specific parameters.
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It should be possible for this data to be shared among several device
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families. The current layout may be insufficiently general, but it is
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amenable to improvement.
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PIXEL_CLOCK
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-----------
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The panel data sheets will give a range of acceptable pixel clocks.
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The fundamental LCDCLK input frequency is divided down by a PCD
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constant in field '.tim2'. It may happen that it is impossible to set
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the pixel clock within this range. A clock which is too slow will
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tend to flicker. For the highest quality image, set the clock as high
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as possible.
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MARGINS
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-------
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These values may be difficult to glean from the panel data sheet. In
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the case of the Sharp panels, the upper margin is explicitly called
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out as a specific number of lines from the top of the frame. The
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other values may not matter as much as the panels tend to
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automatically center the image.
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Sync Sense
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----------
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The sense of the hsync and vsync pulses may be called out in the data
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sheet. On one panel, the sense of these pulses determine the height
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of the visible region on the panel. Most of the Sharp panels use
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negative sense sync pulses set by the TIM2_IHS and TIM2_IVS bits in
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'.tim2'.
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Pel Layout
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----------
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The Sharp color TFT panels are all configured for 16 bit direct color
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modes. The amba-lcd driver sets the pel mode to 565 for 5 bits of
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each red and blue and 6 bits of green.