# GPU/DRM驅動 代碼在driver/gpu/drm下 ~~~ The Direct Rendering Manager (DRM) is a subsystem of the Linux kernel responsible for interfacing with GPUs of modern video cards. DRM exposes an API that user space programs can use to send commands and data to the GPU, and perform operations such as configuring the mode setting of the display. DRM was first developed as the kernel space component of the X Server's Direct Rendering Infrastructure,[1] but since then it has been used by other graphic stack alternatives such as Wayland. ~~~ DRM（圖形渲染架構）是linux的一個內核子系統，負責GPU的交互接口。 DRM暴露API，用戶空間的程序可以發送命令和數據給GPU。 > https://en.wikipedia.org/wiki/Direct_Rendering_Manager#/media/File:Access_to_video_card_without_DRM.svg > 如果沒有DRM：  使用DRM： https://upload.wikimedia.org/wikipedia/commons/thumb/6/6d/Access_to_video_card_with_DRM.svg/1200px-Access_to_video_card_with_DRM.svg.png 查看DRM驅動代碼： ~~~ root@bf756b445919:~/linux/drivers/gpu/drm/sun4i# ls *.c sun4i_backend.c sun4i_dotclock.c sun4i_framebuffer.c sun4i_hdmi_enc.c sun4i_layer.c sun4i_tcon.c sun6i_drc.c sun8i_mixer.c sun4i_crtc.c sun4i_drv.c sun4i_hdmi_ddc_clk.c sun4i_hdmi_tmds_clk.c sun4i_rgb.c sun4i_tv.c sun8i_layer.c ~~~ 參考現成的dts： sun5i-a13-q8-tablet.dts ~~~ #include "sun5i-a13.dtsi" #include "sun5i-reference-design-tablet.dtsi" / { model = "Q8 A13 Tablet"; compatible = "allwinner,q8-a13", "allwinner,sun5i-a13"; panel: panel { compatible = "urt,umsh-8596md-t", "simple-panel"; #address-cells = <1>; #size-cells = <0>; port@0 { reg = <0>; /* TODO: lcd panel uses axp gpio0 as enable pin */ backlight = <&backlight>; #address-cells = <1>; #size-cells = <0>; panel_input: endpoint@0 { reg = <0>; remote-endpoint = <&tcon0_out_lcd>; }; }; }; }; &be0 { status = "okay"; }; &tcon0 { pinctrl-names = "default"; pinctrl-0 = <&lcd_rgb666_pins>; status = "okay"; }; &tcon0_out { tcon0_out_lcd: endpoint@0 { reg = <0>; remote-endpoint = <&panel_input>; }; }; ~~~ 這里引用了compatible = "urt,umsh-8596md-t", "simple-panel"; 在drivers/gpu/drm/panel/panel-simple.c里有很多屏幕型號，選取合適的屏幕型號即可 開啟DRM還需要使能以下內核 1. support for simple panels 2. CMA 3. DMA_CMA 然后需要失能（注釋）掉原來的simplefb在dts中的節點