[OpenWrt-Devel] brcm63xx: Let the CFE partition in HG556a to be writeable

In the HG556a router the partition mtd0, where CFE lives, is read only.
This patch allows this partition to be writeable.

The BCM6358 SoC has two cores, but they are not identical. The second core has 
half icache. 
core0: icache=32kB
core1: icache=16kB

As default the HG556a uses the second core as the main one (configured by CFE).
Since currently there isn't SMP support for using both cores, we want to use the 
one with the best performance.

For using the core0 as the main one, we need to write some bytes at the offset
0x014 of mtd0 (CFE). Therefore we need the mtd0 partition to be writeable.

After setting the core0 as the main one, the performance can increase up to
+20% (tested). The performance gain isn't marginal.

For setting the core0 as the main one in an easy way I wrote a very simple utility:
https://wiki.openwrt.org/_media/media/huawei/tp0set.tar.gz
It can switch from core0 to core1 or vice versa in OpenWrt writing proper bytes
into bcm6358 CFE (fully tested in the HG556a, no bricks).

Signed-off-by: Daniel Gonzalez <dgcbueu@gmail.com>

Hi,

On Wed, Dec 2, 2015 at 9:37 PM, dani <dgcbueu@gmail.com> wrote:
> In the HG556a router the partition mtd0, where CFE lives, is read only.
> This patch allows this partition to be writeable.
>
> The BCM6358 SoC has two cores, but they are not identical. The second core has
> half icache.
> core0: icache=32kB
> core1: icache=16kB
>
> As default the HG556a uses the second core as the main one (configured by CFE).
> Since currently there isn't SMP support for using both cores, we want to use the
> one with the best performance.
>
> For using the core0 as the main one, we need to write some bytes at the offset
> 0x014 of mtd0 (CFE). Therefore we need the mtd0 partition to be writeable.
>
> After setting the core0 as the main one, the performance can increase up to
> +20% (tested). The performance gain isn't marginal.
>
> For setting the core0 as the main one in an easy way I wrote a very simple utility:
> https://wiki.openwrt.org/_media/media/huawei/tp0set.tar.gz
> It can switch from core0 to core1 or vice versa in OpenWrt writing proper bytes
> into bcm6358 CFE (fully tested in the HG556a, no bricks).

To be honest, I'm not very comfortable with making the CFE partition
writable, and rather add code to lzma-loader that switches back to
thread 0, then add lzma-loader for the affected devices.


Jonas

I agree, it would be much better to do the job without touching CFE. In
fact after
changing those bits in CFE to boot always the core0 as the main thread, if
one wants
to return to the OEM firmware it turns out that the board hangs when
loading VoIP
stuff. Probably VoIP stuff is hardcoded in some way that wants the core0
for exclusive
use.

BTW, shouldn't be easier to do the job into the kernel rather than the
lzma-loader?.
And without worrying which boards are affected, just do it for all BCM6358
boards (if
they booted the core1 as the main thread). I can't imagine any user wanting
to run
Openwrt with half icache.

Regards.

2016-01-18 14:15 GMT+01:00 Jonas Gorski <jogo@openwrt.org>:

> Hi,
>
> On Wed, Dec 2, 2015 at 9:37 PM, dani <dgcbueu@gmail.com> wrote:
> > In the HG556a router the partition mtd0, where CFE lives, is read only.
> > This patch allows this partition to be writeable.
> >
> > The BCM6358 SoC has two cores, but they are not identical. The second
> core has
> > half icache.
> > core0: icache=32kB
> > core1: icache=16kB
> >
> > As default the HG556a uses the second core as the main one (configured
> by CFE).
> > Since currently there isn't SMP support for using both cores, we want to
> use the
> > one with the best performance.
> >
> > For using the core0 as the main one, we need to write some bytes at the
> offset
> > 0x014 of mtd0 (CFE). Therefore we need the mtd0 partition to be
> writeable.
> >
> > After setting the core0 as the main one, the performance can increase up
> to
> > +20% (tested). The performance gain isn't marginal.
> >
> > For setting the core0 as the main one in an easy way I wrote a very
> simple utility:
> > https://wiki.openwrt.org/_media/media/huawei/tp0set.tar.gz
> > It can switch from core0 to core1 or vice versa in OpenWrt writing
> proper bytes
> > into bcm6358 CFE (fully tested in the HG556a, no bricks).
>
> To be honest, I'm not very comfortable with making the CFE partition
> writable, and rather add code to lzma-loader that switches back to
> thread 0, then add lzma-loader for the affected devices.
>
>
> Jonas
>