sram_kva
br->br_bd = sram_kva(ring_pa);
var = (volatile uint32_t *)sram_kva(tdt->tdt_var);
(volatile uint32_t *)sram_kva(tdt->tdt_start + drd_offs[i]);
kva = sram_kva(pa);
void * sram_kva(bus_addr_t); /* phys SRAM addr -> CPU pointer */