linux-zen-desktop/Documentation/scsi/53c700.rst

.. SPDX-License-Identifier: GPL-2.0

=======================
The 53c700 Driver Notes
=======================

General Description
===================

This driver supports the 53c700 and 53c700-66 chips.  It also supports
the 53c710 but only in 53c700 emulation mode.  It is full featured and
does sync (-66 and 710 only), disconnects and tag command queueing.

Since the 53c700 must be interfaced to a bus, you need to wrapper the
card detector around this driver.  For an example, see the
NCR_D700.[ch] or lasi700.[ch] files.

The comments in the 53c700.[ch] files tell you which parts you need to
fill in to get the driver working.


Compile Time Flags
==================

A compile time flag is::

	CONFIG_53C700_LE_ON_BE

define if the chipset must be supported in little endian mode on a big
endian architecture (used for the 700 on parisc).


Using the Chip Core Driver
==========================

In order to plumb the 53c700 chip core driver into a working SCSI
driver, you need to know three things about the way the chip is wired
into your system (or expansion card).

1. The clock speed of the SCSI core
2. The interrupt line used
3. The memory (or io space) location of the 53c700 registers.

Optionally, you may also need to know other things, like how to read
the SCSI Id from the card bios or whether the chip is wired for
differential operation.

Usually you can find items 2. and 3. from general spec. documents or
even by examining the configuration of a working driver under another
operating system.

The clock speed is usually buried deep in the technical literature.
It is required because it is used to set up both the synchronous and
asynchronous dividers for the chip.  As a general rule of thumb,
manufacturers set the clock speed at the lowest possible setting
consistent with the best operation of the chip (although some choose
to drive it off the CPU or bus clock rather than going to the expense
of an extra clock chip).  The best operation clock speeds are:

=========  =====
53c700     25MHz
53c700-66  50MHz
53c710     40Mhz
=========  =====

Writing Your Glue Driver
========================

This will be a standard SCSI driver (I don't know of a good document
describing this, just copy from some other driver) with at least a
detect and release entry.

In the detect routine, you need to allocate a struct
NCR_700_Host_Parameters sized memory area and clear it (so that the
default values for everything are 0).  Then you must fill in the
parameters that matter to you (see below), plumb the NCR_700_intr
routine into the interrupt line and call NCR_700_detect with the host
template and the new parameters as arguments.  You should also call
the relevant request_*_region function and place the register base
address into the 'base' pointer of the host parameters.

In the release routine, you must free the NCR_700_Host_Parameters that
you allocated, call the corresponding release_*_region and free the
interrupt.

Handling Interrupts
-------------------

In general, you should just plumb the card's interrupt line in with

request_irq(irq, NCR_700_intr, <irq flags>, <driver name>, host);

where host is the return from the relevant NCR_700_detect() routine.

You may also write your own interrupt handling routine which calls
NCR_700_intr() directly.  However, you should only really do this if
you have a card with more than one chip on it and you can read a
register to tell which set of chips wants the interrupt.

Settable NCR_700_Host_Parameters
--------------------------------

The following are a list of the user settable parameters:

clock: (MANDATORY)
  Set to the clock speed of the chip in MHz.

base: (MANDATORY)
  Set to the base of the io or mem region for the register set. On 64
  bit architectures this is only 32 bits wide, so the registers must be
  mapped into the low 32 bits of memory.

pci_dev: (OPTIONAL)
  Set to the PCI board device.  Leave NULL for a non-pci board.  This is
  used for the pci_alloc_consistent() and pci_map_*() functions.

dmode_extra: (OPTIONAL, 53c710 only)
  Extra flags for the DMODE register.  These are used to control bus
  output pins on the 710.  The settings should be a combination of
  DMODE_FC1 and DMODE_FC2.  What these pins actually do is entirely up
  to the board designer.  Usually it is safe to ignore this setting.

differential: (OPTIONAL)
  Set to 1 if the chip drives a differential bus.

force_le_on_be: (OPTIONAL, only if CONFIG_53C700_LE_ON_BE is set)
  Set to 1 if the chip is operating in little endian mode on a big
  endian architecture.

chip710: (OPTIONAL)
  Set to 1 if the chip is a 53c710.

burst_disable: (OPTIONAL, 53c710 only)
  Disable 8 byte bursting for DMA transfers.