128 lines
4.5 KiB
Markdown
128 lines
4.5 KiB
Markdown
libgfxinit - Native Graphics Initialization
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===========================================
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Introduction and Current State in coreboot
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------------------------------------------
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*libgfxinit* is a library of full-featured graphics initialization
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(aka. modesetting) drivers. It's implemented in SPARK (a subset of
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Ada with formal verification features). While not restricted to in
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any way, it currently only supports Intel's integrated gfx control-
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lers (GMA).
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Currently, it supports the Intel Core i3/i5/i7 processor line and
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will support HDMI and DP on the Atom successor Apollo Lake. At the
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time of writing, Sandy Bridge, Ivy Bridge, and Haswell are veri-
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fied to work within *coreboot*.
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GMA: Framebuffer Configuration
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------------------------------
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*coreboot* supports two different framebuffer setups. The default
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enables the legacy VGA plane in textmode. Due to legacy hardware
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constraints, only the first found display is enabled in this mode.
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(cf. `src/drivers/intel/gma/text_fb/gma.adb`).
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The second option sets up a high-resolution framebuffer with the
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native resolution of the display if only one is detected, or the
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smallest of all resolutions (per dimension) if multiple displays
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are detected. This option is selected by
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`CONFIG_FRAMEBUFFER_KEEP_VESA_MODE`.
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(cf. `src/drivers/intel/gma/hires_fb/gma.adb`).
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In any case, a smaller framebuffer is up-scaled to each display's
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native resolution while keeping aspect ratio.
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GMA: Hook-up in Chipset Initialization
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--------------------------------------
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Both configurations described above implement a procedure
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`GMA.gfxinit()`:
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procedure gfxinit (lightup_ok : out int);
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This procedure is exported as the C function `gma_gfxinit()` as
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follows:
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void gma_gfxinit(int *lightup_ok);
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* `lightup_ok`: returns whether the initialization succeeded `1` or
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failed `0`. Currently, only the case that no display
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could be found counts as failure. A failure at a la-
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ter stage (e.g. failure to train a DP) is not propa-
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gated.
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GMA: Per Board Configuration
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----------------------------
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There are a few Kconfig symbols to consider. To indicate that a
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board can initialize graphics through *libgfxinit*:
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select MAINBOARD_HAS_LIBGFXINIT
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Internal ports share some hardware blocks (e.g. backlight, panel
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power sequencer). Therefore, each board has to select either eDP
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or LVDS as the internal port, if any:
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select GFX_GMA_INTERNAL_IS_EDP # the default, or
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select GFX_GMA_INTERNAL_IS_LVDS
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Boards with a DVI-I connector share the DDC (I2C) pins for both
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analog and digital displays. In this case, *libgfxinit* needs to
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know through which interface the EDID can be queried:
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select GFX_GMA_ANALOG_I2C_HDMI_B # or
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select GFX_GMA_ANALOG_I2C_HDMI_C # or
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select GFX_GMA_ANALOG_I2C_HDMI_D
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Beside Kconfig options, *libgfxinit* needs to know which ports are
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implemented on a board and should be probed for displays. The mapping
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between the physical ports and these entries depends on the hardware
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implementation and can be recovered by testing or studying the output
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of `intelvbttool` or `intel_vbt_decode`.
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Each board has to implement the package `GMA.Mainboard` with a list:
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ports : HW.GFX.GMA.Display_Probing.Port_List;
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or a function returning such a list:
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function ports return HW.GFX.GMA.Display_Probing.Port_List;
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You can select from the following Ports:
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type Port_Type is
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(Disabled, -- optionally terminates the list
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Internal, -- either eDP or LVDS as selected in Kconfig
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DP1,
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DP2,
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DP3,
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HDMI1, -- also DVI-D, or HDMI over DP++
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HDMI2,
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HDMI3,
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Analog); -- legacy VGA port, or analog part of DVI-I
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Each `DPx` and `HDMIx` pair share pins. If they are exposed as DP
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ports, they are usually DP++ (aka. dual-mode DP) ports that can
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also output HDMI signals through passive adapters. In this case,
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both DPx and HDMIx should be listed.
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A good example is the mainboard Kontron/KTQM77, it features two
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DP++ ports (DP2/HDMI2, DP3/HDMI3), one DVI-I port (HDMI1/Analog),
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eDP and LVDS. Due to the constraints mentioned above, only one of
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eDP and LVDS can be enabled. It defines `ports` as follows:
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ports : constant Port_List :=
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(DP2,
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DP3,
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HDMI1,
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HDMI2,
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HDMI3,
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Analog,
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Internal,
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others => Disabled);
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The `GMA.gfxinit()` procedure probes for display EDIDs in the
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given order until all available pipes are taken. That's 1 pipe
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in VGA textmode, 2 pipes in high-resolution mode until Sandy
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Bridge, 3 pipes from Ivy Bridge on.
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