BufferAccessScsiPortControlled Flag Information

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The main reason for the Boolean BufferAccessScsiPortControlled is to give the SCSI port driver the ability to determine if a SCSI miniport driver does not include any coding behavior such as

   DataBufferPointer = x
				

and instead use the ScsiPort{Read,Write}XxxBuffer functions with the data buffer pointer. When the Boolean is set, depending on the operating system and SCSI port driver implementation, the the DataBuffer field in the miniport may not necessarily actually point to the data buffer.

If a miniport always uses the set of ScsiPort{Read,Write}Xxx() functions for I/O to ports and registers (using the character and buffer versions of these functions for for uchar, ushort, ulong data transfers), a miniport driver should set BufferAccessScsiPortControlled to TRUE. This will greatly speed up I/O performance, allowing the SCSI port driver to manage its scatter-gather support much more efficiently.

If a miniport directly touches the memory buffers from an SRB (for example, it sets values in this buffer using some form of "buffer = value" instead of using the ScsiPort{Read,Write}Xxx functions), then the driver should set BufferAccessScsiPortControlled to FALSE (the default value). As a result, the performance of this miniport will be much slower whenever the port driver emulates scatter-gather.