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FPGA Configuration Space
Commit 7b9b75a9 authored by Alessandro Rubini's avatar Alessandro Rubini
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sdbfs/doc: completed iomem sections, minor reorganization 

Signed-off-by: Alessandro Rubini's avatarAlessandro Rubini <rubini@gnudd.com>
parent db0a9259
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sdbfs/doc/sdbfs.in
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......@@ -597,6 +597,15 @@ the module called @i{sdb-iomem.ko} can register those areas to the
@i{sdbfs} module, so you can mount the FPGA and perform register
access from user space using named files.
@c ==========================================================================
@node Supported kernel versions
@section Supported kernel versions
The current version is a development version only, and as such it has
only been built and run under Linux-3.4. In the future I'll check
backward portability -- but I'm sure something changed at 3.2 times,
so backward portability will need some work.
@c ==========================================================================
@node sdbfs.ko
@section sdbfs.ko
......@@ -653,19 +662,82 @@ an @i{sdbfs} image:
@end smallexample
@c ==========================================================================
@node Example use of sdb-iomem
@section Example use of sdb-iomem
@node sdb-iomem.ko
@section sdb-iomem.ko
FIXME
This module can access a region of I/O registers and show it as an
@i{sdbfs} object. The user can specify the memory regions to be
accessed with a module argument.
@c ==========================================================================
@node Supported kernel versions
@section Supported kernel versions
The expected use of this type of filesystem is for driver developers:
if you are working on an SDB-aware FPGA project, you can mount the
internal bus of the FPGA and see the internal registers. Once you know
register offsets, you can ignore the base address of each device
by accessing it by pathname.
The current version is a development version only, and as such it has
only been built and run under Linux-3.4. In the future I'll check
backward portability -- but I'm sure something changed at 3.2 times,
so backward portability will need some work.
This module is currently only a trivial example, and a number of
features are missing. For example, the file-operations for register
access are not yet defined, and the lack of support for subdirectories
is a serious problem to be solved soon. Nonetheless, this approach
may prove very useful over time.
I envision the following steps for development of I/O acess in @i{sdbfs}:
@itemize @bullet
@item FPGA projects should be able to register their internal bus.
@item The names of available @i{sdbfs} devices should appear in @i{sysfs}.
@item A user-space program should know register names for all devices.
@item A web service should publish such register layout files.
@end itemize
Each of these steps is pretty simple in itself, it just takes time to
implement. As for the last step, the central @i{sdb} registry may
offer a DNS service, in order for each vendor to be autonomous in
publishing its own register maps from a vendor-specific host name.
The current implementation does very little, but it is able to
scan a read SDB device and see the internal devices. The specification
of each memory area (at most 8 of them are supported) is:
@example
<name>@@<hex-address>{-<hex-end>|+<hex-size>}[=<hex-entry>]
@end example
All numbers are hexadecimal: the area is specified either as
a range (@code{<addr>-<end>}) or as start-plus-size (@code{<addr>+<size>}).
If the entry point for SDB information is not zero, it must be passed
after an equal (@code{=}) sign.
The following example shows what the current @code{sdb-iomem.ko} can
do, accessing an FPGA driven but the @i{wr-nic} driver (package @i{spec-sw},
version 2.0):
@smallexample
spusa.root# insmod sdb-iomem.ko area=spec0@@0xfd300000+100000=63000
spusa.root# mount -t sdbfs spec0 /mnt
spusa.root# ls -l /mnt
total 0
-r--r--r-- 1 root root 256 Jan 1 1970 WB-VIC-Int.Control
?--------- 1 root root 262144 Jan 1 1970 WR-CORE
?--------- 1 root root 4096 Jan 1 1970 WR-DIO-Core
-r--r--r-- 1 root root 131072 Jan 1 1970 WR-NIC
-r--r--r-- 1 root root 256 Jan 1 1970 WR-TXTSU
spusa.root# rmmod sdb-iomem
spusa.root# insmod sdb-iomem.ko area=spec0@@0xfd300000+100000=62400
spusa.root# mount -t sdbfs spec0 /mnt
spusa.root# ls -l /mnt
total 0
-r--r--r-- 1 root root 256 Jan 1 1970 WB-GPIO-Port
-r--r--r-- 1 root root 256 Jan 1 1970 WB-I2C-Master
-r--r--r-- 1 root root 256 Jan 1 1970 WR-1Wire-master
-r--r--r-- 1 root root 256 Jan 1 1970 WR-DIO-Registers
@end smallexample
The first listing above shows the overall @i{WishBone} bus of
the FPGA. The bridge @code{WR-DIO-Core} should be shown as a
subdirectory. The second listing shows the content of such
subdirectory, by telling @i{sdb-iomem} to access the SDB records
for the @i{dio-core} rather than the top-level one.
@c ##########################################################################
@node Bugs and Missing Features
......@@ -681,19 +753,22 @@ priority or complexity:
@item gensdbfs: more config file options: class and so on.
@item kernel and gensdbfs: support subdirectories. This is not
trivial because of the relative placement of files within the subdir.
trivial in gensdbfs because of the relative placement of files
within the subdir.
@item kernel: add . and .. entries to readdir
@item kernel: support writing to files
@item kernel: support device access (i.e., a real SDB bus)
@item kernel: complete support for device access
@item kernel: read and write bits are not propagated
@item fakedev: show available images in /sys
@item core sdbfs: show available images in /sys
@item lib: kernel space and freestanding is not tested
@item lib: kernel space and freestanding is missing. Also write support
@item lib: write support is missing
@item read-sdb: implement verbose mode and @code{rwxrwxrwx} in long mode
......
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