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| -rw-r--r-- | Documentation/video/tegra_dc_ext.txt | 83 |
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diff --git a/Documentation/video/tegra_dc_ext.txt b/Documentation/video/tegra_dc_ext.txt new file mode 100644 index 000000000000..6fc3394c6652 --- /dev/null +++ b/Documentation/video/tegra_dc_ext.txt @@ -0,0 +1,83 @@ +The Tegra display controller (dc) driver has two frontends that implement +different interfaces: +1. The traditional fbdev interface, implemented in drivers/video/tegra/fb.c +2. A new interface that exposes the unique capabilities of the controller, + implemented in drivers/video/tegra/dc/ext + +The Tegra fbdev capabilities are documented in fb/tegrafb.c [TODO]. This +document will describe the new "extended" dc interface. + +The extended interface is only available when its frontend has been compiled +in, i.e., CONFIG_TEGRA_DC_EXTENSIONS=y. The dc_ext frontend can coexist with +tegrafb, but takes precedence (more on that later). + +The dc_ext frontend's interface to userspace is exposed through a set of +device nodes: one for each controller (generally /dev/tegra_dc_N), and one +"control" node (generally /dev/tegra_dc_ctrl). Communication through these +device nodes is done with special IOCTLs. There is also an event delivery +mechanism; userspace can wait for and receive events with read() or poll(). + +The tegra_dc_N interface is stateful; each fresh open() of the device node +creates a client instance. In order to prevent multiple processes from +"fighting" for the hardware, only one client instance is permitted to control +certain resources at a time, on a first-come, first-serve basis. + +Overview of tegra_dc_N IOCTLs: +SET_NVMAP_FD: This is used to associate your nvmap client with this dc_ext + client instance. This is necessary so that the kernel can + appropriately enforce permissions on nvmap buffers. + +GET_WINDOW: A dc_ext client must call this on each window that it wishes to + control. This strictly enforces a single dc_ext client on a + window at a time. + +PUT_WINDOW: A dc_ext client may call this to release a window previously + reserved with GET_WINDOW. + +FLIP: This ioctl is used to actually display an nvmap surface using one or + more window. Each time a dc_ext client performs a FLIP, the request is + put on a flip queue and executed asynchronously (the FLIP ioctl will + return immediately). Various parameters are available in the + tegra_dc_ext_flip structure. + A dc_ext client may only use this on windows that it has previously + reserved with a successful GET_WINDOW call. + +GET_CURSOR: This is analogous to GET_WINDOW, but for the hardware cursor + instead of a window. + +PUT_CURSOR: This is analogous to PUT_WINDOW, but for the hardware cursor + instead of a window. + +SET_CURSOR_IMAGE: This is used to change the hardware cursor image. May only + be used by a client who has successfully performed a + GET_CURSOR call. + +SET_CURSOR: This is used to actually place the hardware cursor on the screen. + May only be used by a client who has successfully performed a + GET_CURSOR call. + +SET_CSC: This may be used to set a color space conversion matrix on a window. + A dc_ext client may only use this on windows that it has previously + reserved with a successful GET_WINDOW call. + +GET_STATUS: This is used to retrieve general status about the dc. + +GET_VBLANK_SYNCPT: This is used to retrieve the auto-incrementing vblank + syncpoint for the head associated with this dc. + + +Overview of tegra_dc_ctrl IOCTLs: +GET_NUM_OUTPUTS: This returns the number of available output devices on the + system, which may exceed the number of display controllers. + +GET_OUTPUT_PROPERTIES: This returns data about the given output, such as what + kind of output it is, whether it's currently associated + with a head, etc. + +GET_OUTPUT_EDID: This returns the binary EDID read from the device connected + to the given output, if any. + +SET_EVENT_MASK: A dc_ext client may call this ioctl with a bitmask of events + that it wishes to receive. These events will then be + available to that client on a subsequent read() on the same + file descriptor. |