diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/gfx/libgfxinit.md | 27 |
1 files changed, 22 insertions, 5 deletions
diff --git a/Documentation/gfx/libgfxinit.md b/Documentation/gfx/libgfxinit.md index bb4528b958..40f194a4eb 100644 --- a/Documentation/gfx/libgfxinit.md +++ b/Documentation/gfx/libgfxinit.md @@ -88,11 +88,28 @@ know through which interface the EDID can be queried: select GFX_GMA_ANALOG_I2C_HDMI_C # or select GFX_GMA_ANALOG_I2C_HDMI_D -Beside Kconfig options, *libgfxinit* needs to know which ports are -implemented on a board and should be probed for displays. The mapping -between the physical ports and these entries depends on the hardware -implementation and can be recovered by testing or studying the output -of `intelvbttool` or `intel_vbt_decode`. +*libgfxinit* needs to know which ports are implemented on a board +and should be probed for displays. There are two mechanisms to +constrain the list of ports to probe, 1. port presence straps on +the mainboard, and 2. a list of ports provided by *coreboot* (see +below). + +Presence straps are configured via the state of certains pins of +the chipset at reset time. They are documented in the chipset's +datasheets. By default, *libgfxinit* honors these straps for +safety. However, some boards don't implement the straps correctly. +If ports are not strapped as implemented by error, one can select +an option to ignore the straps: + + select GFX_GMA_IGNORE_PRESENCE_STRAPS + +In the opposite case, that ports are strapped as implemented, +but are actually unconnected, one has to make sure that the +list of ports in *coreboot* omits them. + +The mapping between the physical ports and these entries depends on +the hardware implementation and can be recovered by testing or +studying the output of `intelvbttool` or `intel_vbt_decode`. Each board has to implement the package `GMA.Mainboard` with a list: ports : HW.GFX.GMA.Display_Probing.Port_List; |