The solution is a downgrade of the BIOS of the laptop to version 1.10. The problem, in fact, seems to be related to the two latest versions of the BIOS (v1.19 and v1.20). Anyone who does not necessarily need one of these two later BIOS versions, should downgrade to v1.10 to make suspend work.
If your SI1520 does not mount an Intel Core Duo (Yonah) D0 stepping processor (which means mainly those CPUs coded T2x00) you can downgrade to version 1.10. Otherwise you'll have to stick with a BIOS version >= 1.17 and with no touchpad after resume. :-(
v1.19 is officially the initial BIOS for Windows Vista 32bit, so downgrading could bring up problems with Vista. I couldn't find anything wrong in my brief test, but I don't plan to be using Vista much, so that's not so important to me.
Please leave a comment with your experiences with this matter, as it can help other fellow SI1520 owners. Thanks.
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