This driver provides support for the Symbios/LSI Logic 53C8XX PCI SCSI controllers.
Driver features include support for wide SCSI busses and fast10, fast20, fast40 and fast80-dt synchronous data transfers depending on controller capabilities. It also provides generic SCSI features such as tagged command queueing and auto-request sense. This driver is configured by default for a maximum of 446 outstanding commands per bus, 8 LUNs per target and 64 tagged tasks per LUN. These numbers are not so much limited by design as they are considered reasonable values for current SCSI technology. These values can be increased by changing appropriate constants in driver header files (not recommended).
This driver supports the entire Symbios 53C8XX family of PCI SCSI controllers. It also offers the advantage of architectural improvements available only with newer chips.
sym notably handles phase mismatch from SCRIPTS for the 53C896, 53C895A, and 53C1010 cores. As a result, it guarantees that no more than 1 interrupt per IO completion is delivered to the CPU, and that the SCRIPTS processor is never stalled waiting for CPU attention in normal situations.
sym also uses LOAD/STORE SCRIPTS instructions for chips that support it. Only the early 810, 815 and 825 NCR chips do not support LOAD/STORE. Use of LOAD/STORE instead of MEMORY MOVE allows SCRIPTS to access IO registers internal to the chip (no external PCI cycles). As a result, the driver guarantees that no PCI self-mastering will occur for chips that support LOAD/STORE.
LOAD/STORE instructions are also faster than MEMORY MOVE because they do not involve the chip DMA FIFO and are coded on 2 DWORDs instead of 3.
For the early NCR 810, 815 and 825 chips, the driver uses a separate SCRIPTS set that uses MEMORY MOVE instructions for data movements. This is because LOAD/STORE are not supported by these chips.
HVD/LVD capable controllers (895, 895A, 896, and 897) report the actual bus mode in the STEST4 chip IO registers. This feature allows the driver to safely probe against bus mode and to set up the chip accordingly. By default the driver only supports HVD for these chips. For other chips that can support HVD but not LVD, the driver has to probe implementation dependent registers (GPIO) in order to detect HVD bus mode. Only HVD implementations that conform with Symbios Logic recommendations can be detected by the driver. When the SYM_SETUP_SCSI_DIFF kernel option is assigned a value of 1, the driver will also probe against HVD for 825a, 875, 876 and 885 chips, assuming Symbios Logic compatible implementation of HVD.
When the SYM_SETUP_PCI_PARITY is assigned a value of 0, the driver will not enable PCI parity checking for 53C8XX devices. PCI parity checking should not be an option for PCI SCSI controllers, but some systems have been reported to fail using 53C8XX chips, due to spurious or permanent PCI parity errors detected. This option is supplied for convenience but it is neither recommended nor supported.
The generic ncr(4) driver also supports SYM53C8XX based PCI SCSI controllers, except for the SYM53C1010, which is only supported by the sym driver.
By default, when both the ncr(4) and sym drivers are configured, the sym driver takes precedence over the ncr(4) driver. The user can indicate a balancing of chip types between the two drivers by defining the SYM_SETUP_LP_PROBE_MAP kernel configuration option as follows: