Platform: RK3399
OS: Android 6.0
Kernel: 4.4
Version: v2017.04
調試流程
1. 確認板子是否識別到了顯示器的 EDID
echo 0x1f > /sys/module/drm/parameters/debug插拔一下hdmi
然後dmesg | grep drm, 看看裏面的信息是否解析到了edid
[ 405.576876] EDID block is all zeroes
[ 405.577224] rockchip-drm display-subsystem: HDMI-A-1: EDID block 0 invalid.
[ 405.687232] EDID block is all zeroes
[ 405.687590] rockchip-drm display-subsystem: HDMI-A-1: EDID block 0 invalid.EDID = 0
這個就是顯示器被識別爲DVI的主因, 當無法讀出edid時, hdmi驅動可能就會以dvi顯示輸出
2. 測一下hdmi驅動是否可以支持hdmi輸出
使能 CONFIG_DRM_LOAD_EDID_FIRMWARE
（參考 https://markyzq.gitbooks.io/rockchip_drm_integration_helper/content/zh/drm_config_load_firmware.html ）
acer_edid.bin ：http://download.csdn.net/download/dearsq/9905985
將附件的 acer_edid.bin 推到板子上, 以下是android上的例子, linux上也可以進行類似操作
adb push acer_edid.bin /data
adb shell:
mount -o rw,remount /
cp /data/acer_edid.bin /lib/firmware/
echo HDMI-A-1:acer_edid.bin > /sys/module/drm_kms_helper/parameters/edid_firmware採用 acer_edid.bin 模擬 EDID 後分辨率由 DVI 800×600@60HZ 變爲 DVI 1920×1080@60HZ 。但是依舊無法識別 HDMI。
熱插拔信息：
[ 211.948958] [drm:edid_load] Got external EDID base block and 1 extension from "acer_edid.bin" for connector "HDMI-A-1"
[ 211.949953] [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid, remainder is 4
[ 212.066567] [drm:edid_load] Got external EDID base block and 1 extension from "acer_edid.bin" for connector "HDMI-A-1"
[ 212.067598] [drm:drm_edid_block_valid] *ERROR* EDID checksum is invalid, remainder is 4錯誤信息
1. No drm_driver.set_busid() implementation provided by 0x…. Use drm_dev_set_unique() to set the unique
1）dev->driver->set_busid 回調沒有被賦值
2）dev->unique == NULL
set_busid 沒有對應回調是正常的，RK 平臺未對其進行實現，一般在 PC 平臺會對其進行實現。
dev->unique == NULL 不正常。
RK VR SDK 中 DRM 框架太舊了，通過升級 DRM 框架解決。
2. drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c:64:2: error: unknown field ‘fb_dmabuf_export’ specified in initializer
.fb_dmabuf_export = rockchip_fbdev_get_dma_buf,
/home/younix/rk_op_linux_3399/kernel/include/linux/fb.h
/* Export the frame buffer as a dmabuf object */
struct dma_buf *(*fb_dmabuf_export)(struct fb_info *info);3. kernel/drivers/gpu/drm/drm_prime.c:545: undefined reference to ‘dma_buf_get_release_callback_data’
需要對比修改 文件：/home/younix/rk_op_linux_3399/kernel/drivers/dma-buf/dma-buf.c
參考資料
Kernel Doc
https://www.kernel.org/doc/htmldocs/drm/
The DRM/KMS subsystem from a newbie’s point of view
http://events.linuxfoundation.org/sites/events/files/slides/brezillon-drm-kms.pdf
DRM Maintainer 總結的資料：https://markyzq.gitbooks.io/rockchip_drm_integration_helper/content/zh/