If I have to read the VBIOS and add I quirk in the kernel, why the kernel can't
do this by himself ?

Moreover, I saw the previous quirk in the kernel, the max memory clock is often
set to "120000". I guess it stands for 1.2GHz QDR which is equivalent to
4.8GHz. My card, like all the R7 370 are supposed to work at 5.6GHz so this is
a serious lost of performance.

At the moment I will just return my card.