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Gmane
From: Ezequiel Garcia <ezequiel.garcia <at> free-electrons.com>
Subject: [PATCH v2 00/27] Armada 370/XP NAND support
Newsgroups: gmane.linux.drivers.mtd
Date: Friday 18th October 2013 23:02:27 UTC (over 3 years ago)
Hi guys,

This is the v2 of the work implementing NAND support in Armada 370/XP SoCs.
This series is probably not yet complete (see below), but I feel like
we're really closer now :-)

As in the previous version and given I don't have any public datasheet
to show, I'll try to write some of the most relevant parts of the
controller.

* NFCv2 controller background

The controller has a 2176 bytes FIFO buffer. Therefore, in order to support
larger pages, I/O operations on 4 KiB and 8 KiB pages is done with a set of
chunked transfers.

For instance, if we choose a 2048 data chunk and set "BCH" ECC (see below)
we'll have this layout in the pages:

 
------------------------------------------------------------------------------
  | 2048B data | 32B spare | 30B ECC || 2048B data | 32B spare | 30B ECC |
... |
 
------------------------------------------------------------------------------

The driver reads the data and spare portions independently and builds an
internal
buffer with this layout (in the 4 KiB page case):

  ------------------------------------------
  |     4096B data     |     64B spare     |
  ------------------------------------------

Also, for the READOOB command the driver disables the ECC and reads a
'spare + ECC'
OOB, one per chunk read.

  -------------------------------------------------------------------
  |     4096B data     |  32B spare | 30B ECC | 32B spare | 30B ECC |
  -------------------------------------------------------------------

So, in order to achieve reading (for instance), we issue several READ0
commands
(with some additional controller-specific magic) and read two chunks of
2080B
(2048 data + 32 spare) each.
The driver accomodates this data to expose the NAND core a contiguous
buffer
(4096 data + spare) or (4096 + spare + ECC + spare + ECC).

* ECC

The controller has built-in hardware ECC capabilities. In addition it is
configurable between two modes: 1) Hamming, 2) BCH.

Note that the actual BCH mode: BCH-4 or BCH-8 will depend on the way
the controller is configured to transfer the data.

In the BCH mode the ECC code will be calculated for each transfered chunk
and expected to be located (when reading/programming) right after the spare
bytes as the figure above shows.

So, repeating the above scheme, a 2048B data chunk will be followed by 32B
spare, and then the ECC controller will read/write the ECC code (30B in
this case):

  ------------------------------------
  | 2048B data | 32B spare | 30B ECC |
  ------------------------------------

If the ECC mode is 'BCH' then the ECC is *always* 30 bytes long.
If the ECC mode is 'Hamming' the ECC is 6 bytes long, for each 512B block.
So in Hamming mode, a 2048B page will have a 24B ECC.

Despite all of the above, the controller requires the driver to only read
or
write in multiples of 8-bytes, because the data buffer is 64-bits.

* Changes from v1

Aside from several changes based in Brian's feedback, the main changes
from v1 are:

  * The controller's clock source is now fully modeled, see patche 1 to 4.
    Of course, none of those patches should be taken through the mtd
    subsystem, but I'm adding them here for completeness.

  * The chip's cmdfunc() is now independently implemented in each SoC
variant.
    The rationale behind this decision is that 'chunked' I/O is the only
tested
    mode on the Armada370 variant, while the old 'vanilla' I/O is the only
    tested mode on the PXA variant.

    So it's safer to have an implementation for each variant.

  * Added support for BCH-8, in other words: 8-bits of correction in a
512-byte
    region. This is obtained by using a data chunk size of 1024B, thus
doubling
    the ECC BCH strength, as per this ECC engine mechanism.

  * The ECC layout in use, which must be set according to the page size and
    desired ECC strength is now strictly chosen to match only the tested
    combinations.

* Pending stuff

  1. Factory bad blocks handling

  Currently, there's no factory bad block initial scan (when the bad block
  table is missing). The ECC BCH requires to layout the device's pages in
  a splitted "data + OOB + data + OOB" way. This layout being different
from
  the factory layout. In other words,

  Factory view:

  -----------------------------------------------
  |                    Data           |x  OOB   |
  -----------------------------------------------

  Driver's view:

  -----------------------------------------------
  |      Data      | OOB |      Data   x  | OOB |
  -----------------------------------------------

  It can be seen from the above, that the factory bad block marker must be
  searched within the 'data' region, and not in the usual OOB region.

  This seems to be similar to the gpmi-nand driver, yet I really find its
  'bad block swapping' solution odd, so I'm trying to find something
  cleaner.

  2. ECC modeling

  Although I've exposed some ECC information in the ECC layout, I'm still
  not sure why is this needed, or if it's needed at all.

* About this patchset

This is based in l2-mtd's master branch and I've pushed a branch to our
github in case anyone wants to test it:

  https://github.com/MISL-EBU-System-SW/mainline-public/tree/l2-mtd/upstream-nand-v2

Just as the previous, this series is complex and lengthy and any feedback
will
be highly appreciated as well as questions, suggestions or flames. Also, I
hope
our brave PXA regression tester Daniel Mack finds some time to give it a
ride
and report any issues. Daniel: I think owe you several beers already.

* About Mirabox testing

As this work is not considered completely stable, be extra careful when
trying
on the Mirabox. The Mirabox has the bootloader at NAND, and there's some
risk
to brick the board.

That said: I've been using the driver on my Mirabox for several days doing
simple long-run NAND activity and everything worked fine.

If despite this you happen to brick the board, Willy Tarreau has provided
excellent instructions to un-brick the Mirabox:

  http://1wt.eu/articles/mirabox-vs-guruplug/

Thanks!

Ezequiel Garcia (27):
  clk: mvebu: Add Core Divider clock
  ARM: mvebu: Add Core Divider clock device-tree binding
  ARM: mvebu: Add a 2 GHz fixed-clock Armada 370/XP
  ARM: mvebu: Add the core-divider clock to Armada 370/XP
  mtd: nand: pxa3xx: Make config menu show supported platforms
  mtd: nand: pxa3xx: Prevent sub-page writes
  mtd: nand: pxa3xx: Early variant detection
  mtd: nand: pxa3xx: Use chip->cmdfunc instead of the internal
  mtd: nand: pxa3xx: Split FIFO size from to-be-read FIFO count
  mtd: nand: pxa3xx: Replace host->page_size by mtd->writesize
  mtd: nand: pxa3xx: Disable OOB on arbitrary length commands
  mtd: nand: pxa3xx: Use a completion to signal device ready
  mtd: nand: pxa3xx: Add bad block handling
  mtd: nand: pxa3xx: Add driver-specific ECC BCH support
  mtd: nand: pxa3xx: Clear cmd buffer #3 (NDCB3) on command start
  mtd: nand: pxa3xx: Add helper function to set page address
  mtd: nand: pxa3xx: Remove READ0 switch/case falltrough
  mtd: nand: pxa3xx: Split prepare_command_pool() in two stages
  mtd: nand: pxa3xx: Move the data buffer clean to
    prepare_start_command()
  mtd: nand: pxa3xx: Fix SEQIN column address set
  mtd: nand: pxa3xx: Add a read/write buffers markers
  mtd: nand: pxa3xx: Introduce multiple page I/O support
  mtd: nand: pxa3xx: Add multiple chunk write support
  mtd: nand: pxa3xx: Add ECC BCH correctable errors detection
  ARM: mvebu: Add support for NAND controller in Armada 370/XP
  ARM: mvebu: Enable NAND controller in Armada XP GP board
  ARM: mvebu: Enable NAND controller in Armada 370 Mirabox

 .../bindings/clock/mvebu-corediv-clock.txt         |  19 +
 arch/arm/boot/dts/armada-370-mirabox.dts           |  21 +
 arch/arm/boot/dts/armada-370-xp.dtsi               |  26 +
 arch/arm/boot/dts/armada-xp-gp.dts                 |   8 +
 drivers/clk/mvebu/Kconfig                          |   5 +
 drivers/clk/mvebu/Makefile                         |   1 +
 drivers/clk/mvebu/clk-corediv.c                    | 223 +++++++
 drivers/mtd/nand/Kconfig                           |   4 +-
 drivers/mtd/nand/pxa3xx_nand.c                     | 686
++++++++++++++++-----
 include/linux/platform_data/mtd-nand-pxa3xx.h      |   3 +
 10 files changed, 856 insertions(+), 140 deletions(-)
 create mode 100644
Documentation/devicetree/bindings/clock/mvebu-corediv-clock.txt
 create mode 100644 drivers/clk/mvebu/clk-corediv.c

-- 
1.8.1.5


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