There is a display controller in loongson's LS2K1000 SoC and LS7A1000
bridge chip, the display controller is a PCI device. It have two display
pipes but with only one hardware cursor. Each way has a DVO interface
which provide RGB888 signals, vertical & horizontal synchronisations,
data enable and the pixel clock.
Each CRTC is able to drive a 1920x1080@60Hz monitor, the maxmium
resolution is 2048x2048. Loongson display controllers are simple which
require scanout buffers to be physically contiguous.
For LS7A1000 bridge chip, the DC is equipped with a dedicated video RAM
which is typically 64MB or more. In this case, VRAM helper based driver
is intended to be used even through the DC can scanout form system memory.
While LS2K1000 is a SoC which is a typically UMA device, only system
memory is available. Therefore CMA helper based driver is intended to be
used. It is possible to use VRAM helper based driver on LS2K1000 by
carving out part of system memory as VRAM though.
For LS7A1000, there are 4 dedicated GPIOs whose control registers is
located at the DC register space, They are used to emulate two way i2c.
One for DVO0, another for DVO1. LS2K1000 and LS2K0500 SoC don't have such
GPIO hardwared, they grab i2c adapter from other module, either general
purpose GPIO emulated i2c or hardware i2c adapter.
+--++---+
| DDR4 || +---+|
+--+| | PCIe Root complex | LS7A1000 |
|| MC0 | +--++-+++|
+--+ HT 3.0 | || || |
| LS3A4000 |<>| +---++---+ +--++--++-+ +--+
| CPU|<>| | GC1000 | | LSDC |<-->| DDR3 MC |<->| VRAM |
+--+ | ++ +-+--+-++-+ +--+
|| MC1 +---|--|+
+--+| |
| DDR4 | +---+ DVO0 | | DVO1 +--+
+--+ VGA <--|ADV7125|<+ +>|TFP410|--> DVI/HDMI
+---+ +--+
The above picture give a simple usage of LS7A1000, note that the encoder
is not necessary adv7125 or tfp410, other candicates can be ch7034b,
sil9022, ite66121 and lt8618 etc.
By design, the code was written in a NOT fully DT dependent way.
v2: Fixup warnings reported by kernel test robot
v3: Fix more grammar mistakes in Kconfig reported by Randy Dunlap and give
more details about lsdc.
v4:
1) Add dts required and explain why device tree is required.
2) Give more description about lsdc and VRAM helper based driver.
3) Fix warnings reported by kernel test robot.
4) Introduce stride_alignment member into struct lsdc_chip_desc, the
stride alignment is 256 bytes for ls7a1000, ls2k1000 and ls2k0500.
v5:
1) Using writel and readl replace writeq and readq, to fix kernel test
robot report build error on other archtecture.
2) Set default fb format to XRGB at crtc reset time.
v6:
1) Explain why we are not switch to drm dridge subsystem on ls2k1000.
2) Explain why tiny drm driver is not suitable for us.
3) Give a short description of the trival dirty update implement based
on CMA helper.
v7:
1) Remove select I2C_GPIO and I2C_LS2X in Kconfig, it is not ready now
2) Licensing issues are fixed suggested by Krzysztof Kozlowski.
3) Remove lsdc_pixpll_print(), part of it move to debugfs.
4) Set prefer_shadow to true if vram based driver is in using.
5) Replace double blank lines with single line in all files.
6) Verbose cmd line parameter is replaced with drm_dbg()
7) All warnnings reported by ./scripts/checkpatch.pl --strict are fixed
8) Get edid from dtb support is removed as suggested by Maxime Ripard
9) Fix typos and various improvement
v8:
1) Drop damage update implement and its command line.
2) Drop DRM_LSDC_VRAM_DRIVER config option as suggested by Maxime.
3) Deduce DC's identification from its compatible property.
4) Drop the board specific dts patch.
5) Add documention about the display controller device node.
v9:
1) Fix the warnings reported by checkpatch script and fix typos
v10:
1) Pass `make dt_binding_check` validation
2) Fix warnings reported by kernel test robot
v11:
1) Convert the driver to use drm bridge and of graph framework.
2) Dump register value support through debugfs.
3) Select DRM_TTM and DRM_TTM_HELPER in Kconfig which fix linkage
problem when built it into the kernel.
4) Non 64 pixel(256 bytes aligned) horiziontal resolutons got
supported by hacking, default is disabled, enable it by using
'loongson.relax_alignment=1' on kernel cmd line.
5) Various improvement as required by Maxime.
v12:
1) Add gammma support, it is broken because hardware engineer
does not implement this correctly. Using 'loongson.gamma=1' on
the
