Linux Kernel for CM-X270

Overview

Linux kernel for CM-X270 modules provides support for on-board peripherals. Current support coverage is specified at O/S support coverage map page. CompuLab provides ready-to-run binary kernel images, and source code of the modifications and additions made to the Linux kernel to work properly on CM-X270 modules.

Building Linux kernel for CM-X270

Instructions for building Linux kernel for CM-X270 can be found here.

CM-X270 specific additions and changes to Linux kernel 2.6.16

Basic Platform Support

The CM-X270 platform basic support is implemented in the linux/arch/arm/mach-pxa/cm-x270.c. This file includes registration of the devices integrated in the PXA270 SoC, definitions of platform-specific configuration of these devices, platfrom-specific power management code and static mapping for memory mapped IO. This file also includes several routines needed for proper operation of the PCI bridge.

PCI support

The board support for CM-X270 introduces driver for ITE 8152 companion chip and platform specific drivers for proper initialization of ITE 8152 on the CM-X270. The bridge driver implementation resides in linux/arch/arm/mach-pxa/it8152.[ch], parts of the CM-X270 specific initialization code are in linux/arch/arm/mach-pxa/cm-x270-pci.c. There are also changes in linux/arch/arm/kernel/bios32.c that are needed to use the ITE 8152 PCI bridge.

PCI Ethernet Cards

The CompuLab stock kernel does not include built-in support for PCI Ethernet cards. A driver for popular RealTek 8139 card is available as loadable kernel module in Debian Linux for CM-X270 package. The module is called 8139too and can be enabled using

modprobe 8139too

Sound and Touchsreen

UCB1400 AC97 codec with inetgrated touchscreen has several registers, that are not present in AC97 standard. We added initialization of some of these registers and exposure of these registers to user space. This change can be found in linux/sound/pci/ac97/ac97_patch.[ch]

The touchscreen controller driver for UCB1400 is taken from patch 3075/2 in the ARM Linux patch system and slightly modified to suit CM-X270 hardware configuration.

Both audio and touchscreen drivers are modularized if you use default CM-X270 configuration. The following commands enable audio support and touchscreen support respectively:

modprobe snd-pxa2xx-ac97
modprobe ucb1x00-ts

Note, that enabling touchscreen driver without AC97 controller driver is meaningless, since ucb1x00-ts driver uses AC97 bus to access the touchscreen device.

More information about Linux audio subsystem can be found at http://www.alsa-project.org

AC'97 and PCI interaction

The following note is relevant only for cards with 'B' option and without 'A' or 'AT' options.

CM-X270 contains local bus arbitration logic needed to arbiter bus accesses between the CPU and PCI bridge. This arbitration logic and AC97 controller share the same input clock. Linux AC97 driver tests whether there's an audio codec attached to the AC97 bus. If the driver does not find a codec, it disables PXA270 AC97 controller, and its clock altogether. Disabling this clock, in turn, disables the local bus arbitration, and makes PCI bridge useless.

To avoid such unpleasant situation we'd recommend not to enable sound drivers, unless you need them.

NAND flash

CompuLab provides proprietary driver for on-board NAND flash. This driver emulates block device and provides wear-leveling for the flash. The driver uses the same NAND flash layout as the ARMMon bootloader.

Starting at kernel release at October 12, 2006, we also included MTD driver for CM-X270. More information about using MTD on CM-X270 can be found at Linux MTD drivers on CM-X270 page.

Recently we discovered that certain NAND flash chips are not tolerant to any activity on local bus during flash accesses. To overcome this limitation we added an option to NAND flash drivers that allows to ensure there is no bus activity at the time NAND flash is active. This option can be switched on and of with block_irqs parameter of the NAND flash driver.

I2C and SPI

Standard I2C and SPI drivers can be used to access these buses on CM-X270. The I2C drivers are present in Linux kernel 2.6.16, and can be easily enabled using Linux kernel configuration.

As for the SPI drivers, they should be backported to Linux kernel 2.6.16 from 2.6.17 or more recent kernel version.

USB device

USB device controller drivers for PXA270 are not available in mainline kernels, and this is the main reason we do not support USB device functionality on CM-X270. Yet, there several patches available at http://www.rpsys.net/openzaurus/patches/, Handhelds.org, Raphael Assenat site dedicated to Linux on CompuLab boards, and probably others. We never tried these patches, and we don't know which of them will work on CM-X270.

Linux kernel 2.6.24

The CM-X270 platform support was merged into mainline kernel starting from version 2.6.24. There are still some features that are not present in mainline kernel. Most of these features are available in preliminary release of Linux kernel 2.6.24 for CM-X270 (source code only).

Preliminary release of Linux kernel 2.6.24 for CM-X270

• Fixes to suspend/resume functionality
• Change serial port mappings to ensure consistency between CM-X270L and CM-X270W
• Support for UART device integrated into PCI bridge
• Support for Marvell 8686 wireless LAN

Using Wireless LAN

The latest revisions of CM-X270 include wireless LAN module based on Marvell 8686 chipset. The drivers for this chipset can be enabled in the kernel configuration "Device Drivers -> Network device support -> Wireless LAN" menu:

 .config - Linux Kernel v2.6.26-rc3 Configuration
 ──────────────────────────────────────────────────────────────────────────────
  ┌───────────────────────────── Wireless LAN ──────────────────────────────┐
  │  Arrow keys navigate the menu.  <Enter> selects submenus --->.          │
  │  Highlighted letters are hotkeys.  Pressing <Y> includes, <N> excludes, │
  │  <M> modularizes features.  Press <Esc><Esc> to exit, <?> for Help, </> │
  │  for Search.  Legend: [*] built-in  [ ] excluded  <M> module  < >       │
  │ ┌─────────────────────────────────────────────────────────────────────┐ │
  │ │    [ ] Wireless LAN (pre-802.11)                                    │ │
  │ │    [*] Wireless LAN (IEEE 802.11)                                   │ │
  │ │    < >   Aviator/Raytheon 2.4MHz wireless support                   │ │
  │ │    < >   Intel PRO/Wireless 2100 Network Connection                 │ │
  │ │    < >   Intel PRO/Wireless 2200BG and 2915ABG Network Connection   │ │
  │ │    <M>   Marvell 8xxx Libertas WLAN driver support                  │ │
  │ │    < >     Marvell Libertas 8388 USB 802.11b/g cards                │ │
  │ │    < >     Marvell Libertas 8385 CompactFlash 802.11b/g cards       │ │
  │ │    < >     Marvell Libertas 8385 and 8686 SDIO 802.11b/g cards      │ │
  │ │    <M>     Marvell Libertas 8686 G-SPI 802.11b/g cards              │ │
  │ │    [ ]     Enable full debugging output in the Libertas module.     │ │
  │ └────v(+)─────────────────────────────────────────────────────────────┘ │
  ├─────────────────────────────────────────────────────────────────────────┤
  │                    <Select>    < Exit >    < Help >                     │
  └─────────────────────────────────────────────────────────────────────────┘

After the kernel modules are compiled and installed into appropriate place on the CM-X270 root filesystem, the wireless LAN driver can be enabled using "modprobe libertas_spi" command.

The gspi_firmware.tar.gz archive contains firmware that is used by the wireless LAN driver. The contents of this archive should be extracted to /lib/firmware directory in the CM-X270 root filesystem.

You need to have udev installed and running on the CM-X270 for the driver to work properly.

Known problems

• PCI bridge does not always properly resume

Using mainline Linux kernel 2.6.24 on CM-X270

It is possible to use mainline Linux kernel 2.6.24 on CM-X270 "as is". Just keep in mind that the on-board NAND flash can be accessed only using MTD drivers and the serial ports map to different ttys on L and W variants as summarized in the below table:

Serial ports mapping on CM-X270L

UART	SB-X270 port name	Linux tty in 2.6.16	Linux tty in 2.6.24
BTUART	COM-A	ttySA0	ttyS1
FFUART	COM-B	ttySA1	ttyS0
STUART	COM-D	ttySA2	ttyS2
ITE8152 UART	COM-B	ttyS0	not present

Serial ports mapping on CM-X270W

UART	SB-X270 port name	Linux tty in 2.6.16	Linux tty in 2.6.24
FFUART	COM-A	ttySA0	ttyS0
BTUART	COM-D	ttySA1	ttyS1
STUART	COM-C	ttySA2	ttyS2
ITE8152 UART	COM-B	ttyS0	not present

See also

• Getting started with Linux on CM-X270
• Linux Development for XScale modules
• Debian Linux for CM-X270
• Linux MTD drivers on CM-X270