As I experienced the same issue (hangs on reboot, while shutdown is fine) with the latest official kernel, I just tested this patched kernel. Now uname -a reports:
Linux ubuntu-Latitude-E5520 3.2.0-22-generic #35~lp944772 SMP Fri Apr 6 16:15:09 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
Unfortunately this patch did not fix my SandyBridge Dell Latitude E5520 behaviour: shutdown is still fine, reboot hangs exactly the same way as before.
As I still have all beta 1 and 2 kernels installed, I can re-test some previous versions if it makes sense, as I'm pretty sure there was at least one working fine.
As I experienced the same issue (hangs on reboot, while shutdown is fine) with the latest official kernel, I just tested this patched kernel. Now uname -a reports: Latitude- E5520 3.2.0-22-generic #35~lp944772 SMP Fri Apr 6 16:15:09 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux
Linux ubuntu-
Unfortunately this patch did not fix my SandyBridge Dell Latitude E5520 behaviour: shutdown is still fine, reboot hangs exactly the same way as before.
As I still have all beta 1 and 2 kernels installed, I can re-test some previous versions if it makes sense, as I'm pretty sure there was at least one working fine.
Regards