[maemo-users] [maemo-users] Booting from MMC as a de-bricking method

[From: Paule Ecimovic]

Hi, Frantisek,

    Thanks for your answer.

Cheers,

    Paule
----- Original Message ----- 
From: "Frantisek Dufka" <dufkaf at seznam.cz>
To: "Paule Ecimovic" <paule at certrex.net>
Cc: <maemo-users at maemo.org>
Sent: Friday, February 16, 2007 9:38 PM
Subject: Re: [maemo-users] Booting from MMC as a de-bricking method


> Paule Ecimovic wrote:
>> I am most concerned about the bricking scenarios resulting from flashing 
>> a 770 to set it into R&D mode, where the 770 sometimes bricks after 
>> rebooting.
>
> Never hear of this, is this real? What you see on the screen when it 
> boots? How many seconds exactly boot takes since poweron before it reboots 
> again (i.e. in which step mentioned below it stops)?
>
>> Are there bricking scenarios in this reboot situation which involve 
>> corruption beyond MMC reboot?
>
> I'm not sure what you mean by this (and was not answered already). Let's 
> explain how device boots:
>
> 1. bootloader (probably at least two of them, one loads another) 
> initializes some hardware, checks if flasher is connected and finally 
> loads linux kernel from /dev/mtd2. Some small bootloader is stored either 
> in masked ROM or NOR flash directly on OMAP chip, the second one is stored 
> in (NAND) flash - /dev/mtd0
> 2. linux kernel starts, initializes hardware and runs linuxrc from initfs 
> partition (/dev/mtd3)
> 3. initfs (uclibc based system) starts dsme and bme, loads wlan and bt 
> firmware, checks root device name stored in flash (=config partition 
> /dev/mtd1)mounts it and continues boot from that device (via pivot_root 
> [1]). This is where bootmenu modification lives too, it simply allows you 
> to select different root device then stored by flasher.
> 4. /sbin/init starts from the root device and normal linux system boots 
> via rc scripts
>
> This means that if bootloader (/dev/mtd0) or kernel (/dev/mtd2) is 
> corrupted or maybe even config partition (bootloader probably uses it too 
> to store some data - MAC address? list of bad flash blocks? partition 
> layout?) then the device is 'bricked' and bootmenu cannot help since it 
> has no chance to run. Only reflash over usb (or serial) can help.
>
> But normal bricking done by most users and mentioned in previous mail 
> means corrupting rootfs (/dev/mtd4) and this can be solved by booting from 
> anything else (=mmc) via bootmenu.
>
>> Any chance of hard-disk based ITOS for Nokia Internet Tablet's.
>
> Harddisk would not solve anything. Same like when you corrupt your bios on 
> PC.
>
>> but it would allow rebooting in various modes and under various privledge 
>> schemes without the threat of irreparable bricking.
>
> Harddisk is not any better than mmc, both are lock devices used by linux 
> kernel.
>
>
> Regards,
> Frantisek
>
> 1. http://www.die.net/doc/linux/man/man8/pivot_root.8.html