[Prism54-devel] Memory allocation question

[Margit Schubert-While]

In islpci_dev.c :
         /* perform the allocation */
         priv->driver_mem_address = pci_alloc_consistent(priv->pdev,
                                                         HOST_MEM_BLOCK,
                                                         &priv->
                                                         device_host_address);
         if (!priv->driver_mem_address) {
                 /* error allocating the block of PCI memory */
                 printk(KERN_ERR "%s: could not allocate DMA memory, 
aborting!",
                        "prism54");
                 return -1;
         }
         /* assign the Control Block to the first address of the allocated 
area */
         priv->control_block =
             (isl38xx_control_block *) priv->driver_mem_address;
         /* set the Power Save Buffer pointer directly behind the CB */
         priv->device_psm_buffer =
                 priv->device_host_address + CONTROL_BLOCK_SIZE;

Can somebody explain to my poor grey cells why we are using two
different pointers for the CB and PSM buffer ?
(Note driver_mem_address != device_host_address, one is
  physical, one is virtual)

Margit