[Intel-gfx] the questions about adding debug info for modeseting in KMS mode

[yakui_zhao]

Hi, Jesse

    When the X is started in UMS mode, we can see the info related with the mode
setting in the Xorg.log(For example: the detailed EDID info, SDVO device command,
modeline validation). This is very helpful to analyze the issue related with
modesetting.
    But when KMS is used, we have no such info. Maybe it is very useful that we can
get such info in KMS mode. It seems that the following should be added if we hope to
get such info. 
    a. register dump 
    b. the relationship between CRTC and output 
    c. the detailed info related with modeset (For example: the EDID info, SDVO device command
, modeline validatin)

    The item a/b is the static info and I will add them by using debugfs.
    But for the item C, I have the following thoughts.
    1. Add the printk and the info can be obtained by using dmesg. But as 
the kernel log buffer size is limited, we will add the different debug level for DRM. 
       For example: drm_core, drm_driver_debug,drm_kms_debug
       Then the next is to add the debug info for every output device.
    2. Allocate a new buffer, which is used to store the output info related with
the modesetting and then a new proc/sysfs I/F is used to get the info.
       the info related with modesetting will be printed to the allocated buffer. But there
exists an issue. If too much debug info is printed, some info will be lost as the buffer size
is limited. 
       The advantage is that other unrelated info will be avoided.

    Which method is better? I will prefer to add the printk. 

    Welcome the comments.

Thanks.         

      
Best regards.
   Yakui