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Proposal for an interface to pass a DT to the kernel on MIPS

PATCH Gabor Juhos 1 participant 1 message Jan 8, 2013 MIPS

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Gabor Juhos

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Sorry for the duplicated post. The first version did not go through to the e-mail addresses at the linux-mips.org domain due to problems with the SMTP server.

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Hi Everyone!

I'm working on adding device tree support for the ath79 platform. I have experimental patches for several things already however my main problem currently is how the DT should be passed to the kernel.

There were a thread [1] about that on the lmo list in 2011 already, but there were no clear statements about the correct method. I'm using a simple approach during my tests to resolve this problem.

The bootloader puts a magic value to the 'a0' register and the address of the FDT blob is stored in the 'a1' register. I have created the attached patch for U-Boot and that that implements this method. It is against the 'testing' branch of the MIPS U-Boot Custodian Tree [2].

I would like to hear others' opinion about it, before I would invest too much time into an unusable solution. :)

Regards,
Gabor

1. http://www.linux-mips.org/archives/linux-mips/2011-06/msg00059.html
2. git://git.denx.de/u-boot-mips.git
3. bootlog with the patched U-Boot:

Quoted 146 lines

U-Boot> setenv bootargs 'console=ttyATH0,115200 init=/etc/preinit' U-Boot> setenv serverip 192.168.1.254; setenv ipaddr 192.168.1.1 U-Boot> tftp 0xa0800000 tl-wr703n.dtb
dup 1 speed 100
Using eth0 device
TFTP from server 192.168.1.254; our IP address is 192.168.1.1 Filename 'tl-wr703n.dtb'.
Load address: 0xa0800000
Loading: #
done
Bytes transferred = 1957 (7a5 hex)
U-Boot> tftp 0xa0900000 openwrt-ath79-uImage-initramfs-lzma.bin Using eth0 device
TFTP from server 192.168.1.254; our IP address is 192.168.1.1 Filename 'openwrt-ath79-uImage-initramfs-lzma.bin'.
Load address: 0xa0900000
Loading: #################################################################

         #################################################################
         #################################################################
         #################################################################
         #################################################################
         #################################################################
         #################################################################
         ###########################################################

done
Bytes transferred = 2627551 (2817df hex) U-Boot> bootm 0xa0900000 - 0xa0800000
## Booting kernel from Legacy Image at a0900000 ...

   Image Name:   MIPS OpenWrt Linux-3.8-rc2
   Created:      2013-01-07  19:54:05 UTC
   Image Type:   MIPS Linux Kernel Image (lzma compressed)
   Data Size:    2627487 Bytes = 2.5 MiB

Load Address: 80060000
Entry Point: 80060000
Verifying Checksum ... OK
## Flattened Device Tree blob at a0800000
Booting using the fdt blob at 0xa0800000 Uncompressing Kernel Image ... OK
Loading Device Tree to 81f72000, end 81f757a4 ... OK

Starting kernel ...

Linux version 3.8.0-rc2 (juhosg at mag2) (gcc version 4.6.4 20121106 (prerelease) (Linaro GCC 4.6-2012.11) ) #456 Mon Jan 7 20:53:57 CET 2013
ath79: using Device Tree passed by bootloader
bootconsole [early0] enabled
CPU revision is: 00019374 (MIPS 24Kc)
SoC: Atheros AR9330 rev 1
Clocks: CPU:400.000MHz, DDR:400.000MHz, AHB:200.000MHz, Ref:25.000MHz
Determined physical RAM map:
memory: 02000000 @ 80000000 (usable)
memory: 02000000 @ 00000000 (usable)
Initrd not found or empty - disabling initrd
Zone ranges:
Normal [mem 0x00000000-0x1fffffff]
Movable zone start for each node
Early memory node ranges
node 0: [mem 0x00000000-0x01ffffff]
Primary instruction cache 64kB, VIPT, 4-way, linesize 32 bytes.
Primary data cache 32kB, 4-way, VIPT, cache aliases, linesize 32 bytes
Built 1 zonelists in Zone order, mobility grouping on. Total pages: 8128
Kernel command line: console=ttyATH0,115200 init=/etc/preinit rootfstype=squashfs,yaffs,jffs2 noinitrd
PID hash table entries: 128 (order: -3, 512 bytes)
Dentry cache hash table entries: 4096 (order: 2, 16384 bytes)
Inode-cache hash table entries: 2048 (order: 1, 8192 bytes)
__ex_table already sorted, skipping sort
Writing ErrCtl register=00000000
Readback ErrCtl register=00000000
Memory: 26784k/32768k available (2682k kernel code, 5984k reserved, 822k data, 1548k init, 0k highmem)
SLUB: Genslabs=9, HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
NR_IRQS:51
Calibrating delay loop... 265.42 BogoMIPS (lpj=1327104)
pid_max: default: 32768 minimum: 301
Mount-cache hash table entries: 512
NET: Registered protocol family 16
ATH79: using Flattened Device Tree
bio: create slab <bio-0> at 0
cfg80211: Calling CRDA to update world regulatory domain
Switching to clocksource MIPS
NET: Registered protocol family 2
TCP established hash table entries: 512 (order: 0, 4096 bytes)
TCP bind hash table entries: 512 (order: -1, 2048 bytes)
TCP: Hash tables configured (established 512 bind 512)
TCP: reno registered
UDP hash table entries: 256 (order: 0, 4096 bytes)
UDP-Lite hash table entries: 256 (order: 0, 4096 bytes)
NET: Registered protocol family 1
squashfs: version 4.0 (2009/01/31) Phillip Lougher
jffs2: version 2.2. (NAND) (SUMMARY) ?? 2001-2006 Red Hat, Inc.
msgmni has been set to 52
io scheduler noop registered
io scheduler deadline registered (default)
Serial: 8250/16550 driver, 1 ports, IRQ sharing disabled
18020000.uart: ttyATH0 at MMIO 0x18020000 (irq = 11) is a AR933X UART
console [ttyATH0] enabled, bootconsole disabled
console [ttyATH0] enabled, bootconsole disabled
ieee80211 phy0: Atheros AR9330 Rev:0 mem=0xb8100000, irq=2
TCP: cubic registered
NET: Registered protocol family 17
8021q: 802.1Q VLAN Support v1.8
Freeing unused kernel memory: 1548k freed
input: buttons.3 as /devices/buttons.3/input/input0
- preinit -
Press the [f] key and hit [enter] to enter failsafe mode
- regular preinit -
- init -
SCSI subsystem initialized
usbcore: registered new interface driver usbfs
usbcore: registered new interface driver hub
usbcore: registered new device driver usb
PPP generic driver version 2.4.2
ip_tables: (C) 2000-2006 Netfilter Core Team
NET: Registered protocol family 24
ehci_hcd: USB 2.0 'Enhanced' Host Controller (EHCI) Driver
nf_conntrack version 0.5.0 (442 buckets, 1768 max)
ohci_hcd: USB 1.1 'Open' Host Controller (OHCI) Driver
Initializing USB Mass Storage driver...
usbcore: registered new interface driver usb-storage
USB Mass Storage support registered.
usbcore: registered new interface driver ums-alauda
usbcore: registered new interface driver ums-cypress
usbcore: registered new interface driver ums-datafab
usbcore: registered new interface driver ums-freecom
usbcore: registered new interface driver ums-isd200
usbcore: registered new interface driver ums-jumpshot
usbcore: registered new interface driver ums-karma
usbcore: registered new interface driver ums-sddr09
usbcore: registered new interface driver ums-sddr55
usbcore: registered new interface driver ums-usbat

Please press Enter to activate this console.

BusyBox v1.19.4 (2013-01-06 20:43:13 CET) built-in shell (ash) Enter 'help' for a list of built-in commands.

_______ ________ __

 |       |.-----.-----.-----.|  |  |  |.----.|  |_
 |   -   ||  _  |  -__|     ||  |  |  ||   _||   _|
 |_______||   __|_____|__|__||________||__|  |____|
          |__| W I R E L E S S   F R E E D O M
 -----------------------------------------------------
 BARRIER BREAKER (Bleeding Edge, r35026)
 -----------------------------------------------------
  * 1/2 oz Galliano         Pour all ingredients into
  * 4 oz cold Coffee        an irish coffee mug filled
  * 1 1/2 oz Dark Rum       with crushed ice. Stir.
Quoted 3 lines

* 2 tsp. Creme de Cacao
-----------------------------------------------------
root at OpenWrt:/#

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