quoted

If there is no difference between the OMAP3 and the OMAP4 WDT IP, 
just add one entry "ti,omap3-wdt". And then in the OMAP4 DTS you will 
just put : compatible = "ti,omap3-wdt"; or compatible =  
"ti,omap4-wdt", "ti,omap3-wdt";
I'm still a little bit confused about the real need for the 
"ti,omap4-wdt: entry, but it seems to be the way to do it in PPC.

I believe OMAP2, OMAP3 and OMAP4 share the same IP, so how about use 
"ti, omap2-wdt"? and other dts files
put compatible like "ti,omap4-wdt", "ti,omap2-wdt" and "ti,omap4-wdt", 
"ti,omap2-wdt".

Typo, should be "ti,omap3-wdt", "ti,omap2-wdt" and "ti,omap4-wdt", 
"ti,omap2-wdt".

Regards,
Xiao