[Intel-gfx] the questions about adding the default mode for LVDS device in KMS mode

[yakui_zhao]

Hi, Eric/Jesse
    Many users are affected by the issue that the number of modelines in KMS
is less than that in UMS. And we have gotten the root cause that the default mode 
is not added for the LVDS output device.  But how can we fix this issue? 
    
    a. Add the default modes by using CVT/GTF . I have send two patches(CVT/GTF) to
mailing list. If they are merged, we can generate the required modeline based on 
the modeline parameter(hdisplay, vdisplay, vfresh) by using the CVT/GTF algorithm. 
       In such case we will have to add a modeline table, which contains the basic
modeline parameter(hdisplay, vdisplay, vfreshrate). 
       How can we get the modeline table? Do they come from the default mode table in
xserver/hw/xfree86/common/xf86defmodeset.c?
       Are both CVT/GTF algorithm used to generate the modeline for the given modeline 
parameter?(hdisplay, vdisplay, vfreshrate). If only one algorithm is enough, which should
be used? 
     
       At the same time there exists another issue. If the modeline is generated by using
CVT/GTF, the parameter is different with that defined in default mode table.
      For example: 1024*768 at 60HZ
       CVT: hdisplay=1024, hsync_start=1072 hsync_end=1176, htotal=1328
	    vdsipaly=768, vsync_start=771, vsync_end=775, vtotal=798
	    dotclk = 63.50MHz
       GTF: hdisplay=1024, hsync_start=1080 hsync_end=1184, htotal=1344
	    vdsipaly=768, vsync_start=769, vsync_end=772, vtotal=795
	    dotclk = 64.11MHz
       default table:
            hdisplay=1024, hsync_start=1048 hsync_end=1184, htotal=1344
	    vdsipaly=768, vsync_start=771, vsync_end=777, vtotal=806
	    dotclk = 65MHz
            65000, 1024,1048,1184,1344,0, 768,771,777,806
       
       Can the above difference be ignored?

    b. Is the default mode table generated when drm device is created or dynamically created for every
output device? 
	If the default mode table is generated for the drm device, it is duplicated and then added to 
the output device when it is required. The advantage is that the default mode table is created only once.
But the disadvantage is that it will use more memory space to store the default mode table.
        If the default mode table is dynamically generated for the output device. The advantage is that
it can save some memory space. But the disadvantage is that the default mode table will be generated several
times if more than two output devices requires the default mode. If the default mode table is generated
by using CVT/GTF, it is duplicated.
        
        Which method is better?

Thanks.         

      
Best regards.
   Yakui