135 lines
4.6 KiB
ReStructuredText
135 lines
4.6 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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=======================
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The 53c700 Driver Notes
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=======================
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General Description
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===================
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This driver supports the 53c700 and 53c700-66 chips. It also supports
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the 53c710 but only in 53c700 emulation mode. It is full featured and
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does sync (-66 and 710 only), disconnects and tag command queueing.
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Since the 53c700 must be interfaced to a bus, you need to wrapper the
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card detector around this driver. For an example, see the
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NCR_D700.[ch] or lasi700.[ch] files.
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The comments in the 53c700.[ch] files tell you which parts you need to
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fill in to get the driver working.
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Compile Time Flags
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==================
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A compile time flag is::
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CONFIG_53C700_LE_ON_BE
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define if the chipset must be supported in little endian mode on a big
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endian architecture (used for the 700 on parisc).
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Using the Chip Core Driver
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==========================
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In order to plumb the 53c700 chip core driver into a working SCSI
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driver, you need to know three things about the way the chip is wired
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into your system (or expansion card).
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1. The clock speed of the SCSI core
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2. The interrupt line used
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3. The memory (or io space) location of the 53c700 registers.
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Optionally, you may also need to know other things, like how to read
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the SCSI Id from the card bios or whether the chip is wired for
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differential operation.
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Usually you can find items 2. and 3. from general spec. documents or
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even by examining the configuration of a working driver under another
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operating system.
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The clock speed is usually buried deep in the technical literature.
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It is required because it is used to set up both the synchronous and
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asynchronous dividers for the chip. As a general rule of thumb,
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manufacturers set the clock speed at the lowest possible setting
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consistent with the best operation of the chip (although some choose
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to drive it off the CPU or bus clock rather than going to the expense
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of an extra clock chip). The best operation clock speeds are:
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========= =====
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53c700 25MHz
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53c700-66 50MHz
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53c710 40Mhz
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========= =====
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Writing Your Glue Driver
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========================
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This will be a standard SCSI driver (I don't know of a good document
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describing this, just copy from some other driver) with at least a
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detect and release entry.
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In the detect routine, you need to allocate a struct
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NCR_700_Host_Parameters sized memory area and clear it (so that the
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default values for everything are 0). Then you must fill in the
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parameters that matter to you (see below), plumb the NCR_700_intr
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routine into the interrupt line and call NCR_700_detect with the host
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template and the new parameters as arguments. You should also call
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the relevant request_*_region function and place the register base
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address into the 'base' pointer of the host parameters.
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In the release routine, you must free the NCR_700_Host_Parameters that
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you allocated, call the corresponding release_*_region and free the
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interrupt.
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Handling Interrupts
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-------------------
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In general, you should just plumb the card's interrupt line in with
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request_irq(irq, NCR_700_intr, <irq flags>, <driver name>, host);
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where host is the return from the relevant NCR_700_detect() routine.
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You may also write your own interrupt handling routine which calls
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NCR_700_intr() directly. However, you should only really do this if
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you have a card with more than one chip on it and you can read a
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register to tell which set of chips wants the interrupt.
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Settable NCR_700_Host_Parameters
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--------------------------------
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The following are a list of the user settable parameters:
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clock: (MANDATORY)
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Set to the clock speed of the chip in MHz.
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base: (MANDATORY)
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Set to the base of the io or mem region for the register set. On 64
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bit architectures this is only 32 bits wide, so the registers must be
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mapped into the low 32 bits of memory.
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pci_dev: (OPTIONAL)
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Set to the PCI board device. Leave NULL for a non-pci board. This is
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used for the pci_alloc_consistent() and pci_map_*() functions.
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dmode_extra: (OPTIONAL, 53c710 only)
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Extra flags for the DMODE register. These are used to control bus
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output pins on the 710. The settings should be a combination of
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DMODE_FC1 and DMODE_FC2. What these pins actually do is entirely up
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to the board designer. Usually it is safe to ignore this setting.
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differential: (OPTIONAL)
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Set to 1 if the chip drives a differential bus.
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force_le_on_be: (OPTIONAL, only if CONFIG_53C700_LE_ON_BE is set)
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Set to 1 if the chip is operating in little endian mode on a big
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endian architecture.
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chip710: (OPTIONAL)
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Set to 1 if the chip is a 53c710.
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burst_disable: (OPTIONAL, 53c710 only)
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Disable 8 byte bursting for DMA transfers.
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