[PATCH] kernel: Disable IXP4xx physmap by default

Linus Walleij linus.walleij at linaro.org
Thu Apr 15 09:48:12 BST 2021

On Thu, Apr 15, 2021 at 8:03 AM Raylynn Knight <rayknight at me.com> wrote:

> Now that there is DTS support in the mainline kernel for IXP4xx what is the
> recommended approach for re-enabling support for devices with adequate
> Flash and RAM (i.e. ADI Engineering SBC250, Gateworks Avila and Cambria,
> US Robotics USR8200)?

The right approach is to finish the driver migration in the mainline kernel,
so that all of the platform can be probed from DTS files.

The two main drivers to be fixed are:

- The ethernet phy DTS binding (I was planning to work on this but you
  know, time)

- The PCI host complex

I think complete migration should be doable, some minor drivers may
need some extra work after that but these two things would make
complete device tree migration possible for all boards.
So if we fix this we can start to re-enable IXP4xx on top.

(Then there will be some fringe drivers, for example the NSLU2
beeper driver...)

There is a bigger issue for complete modernization of the architecture.
The PCI host is a complicated beast because accesses to PCI on
IXP4xx are crippled. You can see that in this file:
the _indirect versions of generic readw/writel etc are really serious
stuff. My idea for a long-term solution is to create some infrastructure
for runtime patching. A really complicated problem for someone
who has time to spend.

> There is already a DTS available for the Gateworks Cambria GW2358.
> I also have access to Edgewater Networks, Secure Computing and
> WatchGuard devices that use the IXP4xx processor and have adequate
> Flash and RAM.

I think making device trees for all of them should be doable once we
have migrated ethernet and PCI host to device tree.

Now that I know there is interest I might get more motivation to
work on it :) can I include you on CC if I post patches for

Linus Walleij

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