1.. SPDX-License-Identifier: GPL-2.0
2
3=======================
4The 53c700 Driver Notes
5=======================
6
7General Description
8===================
9
10This driver supports the 53c700 and 53c700-66 chips.  It also supports
11the 53c710 but only in 53c700 emulation mode.  It is full featured and
12does sync (-66 and 710 only), disconnects and tag command queueing.
13
14Since the 53c700 must be interfaced to a bus, you need to wrapper the
15card detector around this driver.  For an example, see the
16NCR_D700.[ch] or lasi700.[ch] files.
17
18The comments in the 53c700.[ch] files tell you which parts you need to
19fill in to get the driver working.
20
21
22Compile Time Flags
23==================
24
25A compile time flag is::
26
27	CONFIG_53C700_LE_ON_BE
28
29define if the chipset must be supported in little endian mode on a big
30endian architecture (used for the 700 on parisc).
31
32
33Using the Chip Core Driver
34==========================
35
36In order to plumb the 53c700 chip core driver into a working SCSI
37driver, you need to know three things about the way the chip is wired
38into your system (or expansion card).
39
401. The clock speed of the SCSI core
412. The interrupt line used
423. The memory (or io space) location of the 53c700 registers.
43
44Optionally, you may also need to know other things, like how to read
45the SCSI Id from the card bios or whether the chip is wired for
46differential operation.
47
48Usually you can find items 2. and 3. from general spec. documents or
49even by examining the configuration of a working driver under another
50operating system.
51
52The clock speed is usually buried deep in the technical literature.
53It is required because it is used to set up both the synchronous and
54asynchronous dividers for the chip.  As a general rule of thumb,
55manufacturers set the clock speed at the lowest possible setting
56consistent with the best operation of the chip (although some choose
57to drive it off the CPU or bus clock rather than going to the expense
58of an extra clock chip).  The best operation clock speeds are:
59
60=========  =====
6153c700     25MHz
6253c700-66  50MHz
6353c710     40Mhz
64=========  =====
65
66Writing Your Glue Driver
67========================
68
69This will be a standard SCSI driver (I don't know of a good document
70describing this, just copy from some other driver) with at least a
71detect and release entry.
72
73In the detect routine, you need to allocate a struct
74NCR_700_Host_Parameters sized memory area and clear it (so that the
75default values for everything are 0).  Then you must fill in the
76parameters that matter to you (see below), plumb the NCR_700_intr
77routine into the interrupt line and call NCR_700_detect with the host
78template and the new parameters as arguments.  You should also call
79the relevant request_*_region function and place the register base
80address into the 'base' pointer of the host parameters.
81
82In the release routine, you must free the NCR_700_Host_Parameters that
83you allocated, call the corresponding release_*_region and free the
84interrupt.
85
86Handling Interrupts
87-------------------
88
89In general, you should just plumb the card's interrupt line in with
90
91request_irq(irq, NCR_700_intr, <irq flags>, <driver name>, host);
92
93where host is the return from the relevant NCR_700_detect() routine.
94
95You may also write your own interrupt handling routine which calls
96NCR_700_intr() directly.  However, you should only really do this if
97you have a card with more than one chip on it and you can read a
98register to tell which set of chips wants the interrupt.
99
100Settable NCR_700_Host_Parameters
101--------------------------------
102
103The following are a list of the user settable parameters:
104
105clock: (MANDATORY)
106  Set to the clock speed of the chip in MHz.
107
108base: (MANDATORY)
109  Set to the base of the io or mem region for the register set. On 64
110  bit architectures this is only 32 bits wide, so the registers must be
111  mapped into the low 32 bits of memory.
112
113pci_dev: (OPTIONAL)
114  Set to the PCI board device.  Leave NULL for a non-pci board.  This is
115  used for the pci_alloc_consistent() and pci_map_*() functions.
116
117dmode_extra: (OPTIONAL, 53c710 only)
118  Extra flags for the DMODE register.  These are used to control bus
119  output pins on the 710.  The settings should be a combination of
120  DMODE_FC1 and DMODE_FC2.  What these pins actually do is entirely up
121  to the board designer.  Usually it is safe to ignore this setting.
122
123differential: (OPTIONAL)
124  Set to 1 if the chip drives a differential bus.
125
126force_le_on_be: (OPTIONAL, only if CONFIG_53C700_LE_ON_BE is set)
127  Set to 1 if the chip is operating in little endian mode on a big
128  endian architecture.
129
130chip710: (OPTIONAL)
131  Set to 1 if the chip is a 53c710.
132
133burst_disable: (OPTIONAL, 53c710 only)
134  Disable 8 byte bursting for DMA transfers.
135