I2C/SGPIO on Marvell 88SE6440 (mvsas)

Dear All,

I have one Adaptec 1405 card with a Marvell 88SE6440 chip (mvsas). The card has one SFF-8087 connector with integrated I2C/SGPIO. On the other side my cable is SFF-8484 and connected to one simple 4x SAS/SATA backplane without RAID logic (sas/sata lines are directly routed to HDDs).

The problem with the backplane is that it controls SATA's pin 15 and the hard drives do not spin-up unless instructed to. This operation is handled by a PCA9556 chip located directly on the backplane.

My question is, how can I talk to this PCA9556 chip using mvsas driver? Or alternatively, where to get info, what needs to be written for "mvsas" to get this working?

Sincerely,
Dennis