Kernel choices for 824x with ext3 FS

Kernel choices for 824x with ext3 FS

[Ron Bianco]

Greetings,

I've been scouting out kernel alternatives for porting to our custom 8240 board.
We've been running a port of 2.3.16 for a few years now, but need to upgrade for
a couple of reasons.
I've been looking at Denx's 2.4.4 port, linuxppc 2.5, linux 2.4.22 and the
latest 2.6.0-test trees.

BTW, many thanks to Wolfgang Denk for making available the ELDK and his ( and
others ) embedded PPC specific work!

Unfortunately we can't use 2.4.4 as ext3 FS support is not present.
FYI, we may also have a need to use RTAI.

I am looking for some advice on which tree to use as a starting point for a new
embedded ppc port.
It is desirable to use the most up to date, yet robust for ppc, kernel possible
and this is somewhat awkward timing vis a vis the status of the 2.6.0 kernel.
But most pertinent ppc related patches seem to be included in 2.6.0 now along
with other enhancements, such as reduced latency, that are not present in
2.4.22.   So it is a bit of a quandary for me, and perhaps for others as well.

A short? hardware overview:
The board is a bare bones design used strictly for scsi ( symbios 53c895 ),
ethernet ( intel 82559 ), and interfaces to our custom backplane in a digital
audio matrix mixer.  The board's flash chip and boot sequence are controlled by
the system's main DSP board.
The backplane interface is via a 16k word dual port RAM and the firmware images
are transferred to SDRAM during startup thru it.
A rather unique situation and it is complicated by the fact that the board has
no UART.  In hindsight a very dumb omission, but this was worked around by
hacking a dummy serial port buffer scheme.
Anyway, it's been working well, and we've managed to cope with the rather large
linux 2.3.x interrupt latency variance in our custom device driver that handles
the backplane interface.   A driver improvement to use the 8240 DMA units helped
too, but there is still a 166 usec. interrupt and the driver can only cope with
getting behind up to 3 interrupts.
We used raw access to the scsi disks with a primitve 'FS' for audio storage and
had done some hacks to the driver set to enable auto switching quickly to a
backup drive if the active drive failed.  The system can be powered down at any
time, which precluded using a non-journalled FS.

But now we have new product specifications that requires the use of a journaling
FS and hardware RAID level 1, and I wish to take the opportunity to improve the
interrupt latency situation too.

Any comments appreciated.

regards, Ron


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Re: Kernel choices for 824x with ext3 FS

[Wolfgang Denk]

Dear Ron,

in message <000101c3980c$2811a3a0$4d00a8c0@warp-speed> you wrote:
>
> I've been looking at Denx's 2.4.4 port, linuxppc 2.5, linux 2.4.22 and the
> latest 2.6.0-test trees.

You can also use our linuxppc_2_4_devel tree from CVS (version 2.4.20)

> BTW, many thanks to Wolfgang Denk for making available the ELDK and his ( and
> others ) embedded PPC specific work!

You are welcome :-)

> Unfortunately we can't use 2.4.4 as ext3 FS support is not present.
> FYI, we may also have a need to use RTAI.

We use our linuxppc_2_4_devel tree to validate the PowerPC port of RTAI.

> It is desirable to use the most up to date, yet robust for ppc, kernel possible
> and this is somewhat awkward timing vis a vis the status of the 2.6.0 kernel.
> But most pertinent ppc related patches seem to be included in 2.6.0 now along
> with other enhancements, such as reduced latency, that are not present in
> 2.4.22.   So it is a bit of a quandary for me, and perhaps for others as well.

I think our 2.4.20 tree is pretty stable; this is one reason we don't
support more recent versions yet.

Best regards,

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
Nothing ever becomes real until it is experienced.       - John Keats

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RE: Kernel choices for 824x with ext3 FS

[Ron Bianco]

> >
> > I've been looking at Denx's 2.4.4 port, linuxppc 2.5, linux 2.4.22 and the
> > latest 2.6.0-test trees.
>
> You can also use our linuxppc_2_4_devel tree from CVS (version 2.4.20)

Thanks, I wasn't sure what that module name referred to or the tree's status.
I just did a cvs checkout on it.
I suppose it is a superset of the linux_2_4_devel tree at penguinppc.org?

> > Unfortunately we can't use 2.4.4 as ext3 FS support is not present.
> > FYI, we may also have a need to use RTAI.
>
> We use our linuxppc_2_4_devel tree to validate the PowerPC port of RTAI.

Very cool and helpful.
I see other advantages to 'following the lead' of folks that are much more
kernel savvy, as well.
It's probably best for us to go with that 2.4.20 for now.
Our specific patches for our rather odd ball board should be easier on 2.6.0
later, once I get some experience with 2.4.20.

> I think our 2.4.20 tree is pretty stable; this is one reason we don't
> support more recent versions yet.

Yes that is a major concern.  Unfortunately we still don't have much in the way
of resources to contribute to general kernel debugging or development.  But I
will post what might be of interest as things proceed.

Cheers, Ron


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Re: Kernel choices for 824x with ext3 FS

[Wolfgang Denk]

Dear Ron,

in message <000701c39823$d04388b0$4d00a8c0@warp-speed> you wrote:
>
> Thanks, I wasn't sure what that module name referred to or the tree's status.
> I just did a cvs checkout on it.
> I suppose it is a superset of the linux_2_4_devel tree at penguinppc.org?

Not exactly a superset, as we froze the version after 2.4.20. But  we
added / fixed a couple of things. So probably the best descritpion is
to say it's a branch off the "official" tree based on 2.4.20

Best regards,

Wolfgang Denk

--
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd@denx.de
It's a small world, but I wouldn't want to paint it.

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