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Re: [PATCH] Linux loader for OLPC

From: Bean
Subject: Re: [PATCH] Linux loader for OLPC
Date: Sun, 13 Apr 2008 23:18:31 +0800

On Sun, Apr 13, 2008 at 7:41 PM, Robert Millan <address@hidden> wrote:
> On Thu, Apr 03, 2008 at 11:19:32PM +0800, Bean wrote:
>  > Hi,
>  >
>  > The new patch add support for the nand flash device in OLPC. However,
>  > the flash use jffs2 file system, so you can't list file in it yet, but
>  > you can dump the disk with hexdump.
>  >
>  > This patch also include an improvement for hexdump that would allow it
>  > to dump device as well as file, for example:
>  >
>  > hexdump (nand)
>  I'm surprised that the nand works via ieee1275 calls.  See my comment in
>  cmain.c:
>   if (is_olpc)
>     {
>       /* OLPC / XO laptops have three kinds of storage devices:
>          - NAND flash.  These are accessible via OFW callbacks, but:
>            - Follow strange semantics, imposed by hardware constraints.
>            - Its ABI is undocumented, and not stable.
>            They lack "device_type" property, which conveniently makes GRUB
>            skip them.
>          - USB drives.  Not accessible, because OFW shuts down the controller
>            in order to prevent collisions with applications accessing it
>            directly.  Even worse, attempts to access it will NOT return
>            control to the caller, so we have to avoid probing them.
>          - SD cards.  These work fine.
>          To avoid brekage, we only need to skip USB probing.  However,
>          since detecting SD cards is more reliable, we do that instead.
>       */
>       grub_ieee1275_set_flag (GRUB_IEEE1275_FLAG_OFDISK_SDCARD_ONLY);
>     }
>  but your patch doesn't seem to disable the 
>  hack.
>  Also, I'm not sure how stable this will be.  Perhaps it breaks in the future
>  with firmware updates :-(

nand access is different from normal disk, it uses pio-read to read a
page which is normally 2048 bytes.

: pio-read  ( adr len page# offset -- )

nand device doesn't have device_type property, it won't be detected by
ofdisk.c, so i put it in a separate module nand.c.

as for GRUB_IEEE1275_FLAG_OFDISK_SDCARD_ONLY, perhaps we can rename it
GRUB_IEEE1275_FLAG_OLPC to indicate OLPC platform, we might need to
use it for other things.

>  > I also add a new function grub_getcrc32 in kern/misc.c, this function
>  > is useful in many places, for example, jffs2 use it to verify data. A
>  > new command crc is also included that would allow user to calculate
>  > the crc checksum of file.
>  That sounds very useful.  But I'm not sure if it's a good idea to put it in
>  kernel.  Perhaps a "crypt" module would be better?  (so that we can add more
>  crypto-related functions when we support LUKS, etc).

That's a good idea.


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