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  19. Jan 10, 2006
    • Alan Cox's avatar
      [PATCH] TTY layer buffering revamp · 33f0f88f
      Alan Cox authored 
      

The API and code have been through various bits of initial review by
serial driver people but they definitely need to live somewhere for a
while so the unconverted drivers can get knocked into shape, existing
drivers that have been updated can be better tuned and bugs whacked out.

This replaces the tty flip buffers with kmalloc objects in rings. In the
normal situation for an IRQ driven serial port at typical speeds the
behaviour is pretty much the same, two buffers end up allocated and the
kernel cycles between them as before.

When there are delays or at high speed we now behave far better as the
buffer pool can grow a bit rather than lose characters. This also means
that we can operate at higher speeds reliably.

For drivers that receive characters in blocks (DMA based, USB and
especially virtualisation) the layer allows a lot of driver specific
code that works around the tty layer with private secondary queues to be
removed. The IBM folks need this sort of layer, the smart serial port
people do, the virtualisers do (because a virtualised tty typically
operates at infinite speed rather than emulating 9600 baud).

Finally many drivers had invalid and unsafe attempts to avoid buffer
overflows by directly invoking tty methods extracted out of the innards
of work queue structs. These are no longer needed and all go away. That
fixes various random hangs with serial ports on overflow.

The other change in here is to optimise the receive_room path that is
used by some callers. It turns out that only one ldisc uses receive room
except asa constant and it updates it far far less than the value is
read. We thus make it a variable not a function call.

I expect the code to contain bugs due to the size alone but I'll be
watching and squashing them and feeding out new patches as it goes.

Because the buffers now dynamically expand you should only run out of
buffering when the kernel runs out of memory for real.  That means a lot of
the horrible hacks high performance drivers used to do just aren't needed any
more.

Description:

tty_insert_flip_char is an old API and continues to work as before, as does
tty_flip_buffer_push() [this is why many drivers dont need modification].  It
does now also return the number of chars inserted

There are also

tty_buffer_request_room(tty, len)

which asks for a buffer block of the length requested and returns the space
found.  This improves efficiency with hardware that knows how much to
transfer.

and tty_insert_flip_string_flags(tty, str, flags, len)

to insert a string of characters and flags

For a smart interface the usual code is

    len = tty_request_buffer_room(tty, amount_hardware_says);
    tty_insert_flip_string(tty, buffer_from_card, len);

More description!

At the moment tty buffers are attached directly to the tty.  This is causing a
lot of the problems related to tty layer locking, also problems at high speed
and also with bursty data (such as occurs in virtualised environments)

I'm working on ripping out the flip buffers and replacing them with a pool of
dynamically allocated buffers.  This allows both for old style "byte I/O"
devices and also helps virtualisation and smart devices where large blocks of
data suddenely materialise and need storing.

So far so good.  Lots of drivers reference tty->flip.*.  Several of them also
call directly and unsafely into function pointers it provides.  This will all
break.  Most drivers can use tty_insert_flip_char which can be kept as an API
but others need more.

At the moment I've added the following interfaces, if people think more will
be needed now is a good time to say

 int tty_buffer_request_room(tty, size)

Try and ensure at least size bytes are available, returns actual room (may be
zero).  At the moment it just uses the flipbuf space but that will change.
Repeated calls without characters being added are not cumulative.  (ie if you
call it with 1, 1, 1, and then 4 you'll have four characters of space.  The
other functions will also try and grow buffers in future but this will be a
more efficient way when you know block sizes.

 int tty_insert_flip_char(tty, ch, flag)

As before insert a character if there is room.  Now returns 1 for success, 0
for failure.

 int tty_insert_flip_string(tty, str, len)

Insert a block of non error characters.  Returns the number inserted.

 int tty_prepare_flip_string(tty, strptr, len)

Adjust the buffer to allow len characters to be added.  Returns a buffer
pointer in strptr and the length available.  This allows for hardware that
needs to use functions like insl or mencpy_fromio.

Signed-off-by: default avatarAlan Cox <alan@redhat.com>
Cc: Paul Fulghum <paulkf@microgate.com>
Signed-off-by: default avatarHirokazu Takata <takata@linux-m32r.org>
Signed-off-by: default avatarSerge Hallyn <serue@us.ibm.com>
Signed-off-by: default avatarJeff Dike <jdike@addtoit.com>
Signed-off-by: default avatarJohn Hawkes <hawkes@sgi.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: default avatarAdrian Bunk <bunk@stusta.de>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      33f0f88f
  21. Jan 04, 2006
  23. Nov 24, 2005
  25. Oct 28, 2005
  27. Sep 22, 2005
  29. Sep 12, 2005
  31. Sep 08, 2005
    • Ian Abbott's avatar
      [PATCH] USB ftdi_sio: New IDs for ELV, Xsens and Falcom products · e6ac4a40
      Ian Abbott authored 
      

This patch for the ftdi_sio driver adds a bunch of new devices and fixes
an incorrect PID:

o Fix PID for ELV UO100 (the PID was in fact for ELV UR100).
o Add PID ELV UR100 (see above) and ELV ALC 8500 Expert.
o Add a whole bunch of other PIDs for ELV USB devices, commented out for
   now as they may be used by other drivers eventually.  (Christian Abt
   of ELV.de submitted a full list of devices including an indication of
   which set of drivers are used by default in the MS Windows world.  We
   decided to comment out the devices that use FTDI's D2XX Windows
   drivers by default.)
o Add PIDs for eight devices from Xsens Technologies BV (submitted in a
   patch against 2.6.12.2 by Patrick Riphagen).
o Add PID for Falcom Samba GPRS modem (submitted by Sebastian Schubert).

Signed-off-by: default avatarIan Abbott <abbotti@mev.co.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
      e6ac4a40
    • Ian Abbott's avatar
      [PATCH] USB ftdi_sio: user specified VID/PID · fdcb0a0f
      Ian Abbott authored 
      

ftdi_sio: Support one user specified vendor and product ID via a couple
of new module parameters.

Signed-off-by: default avatarIan Abbott <abbotti@mev.co.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
      fdcb0a0f
  33. Jul 29, 2005