Re: [PATCH] ARM: l2x0: add L210 write allocate override flag

[Linus Walleij <linus.walleij@linaro.org>]

On Mon, Mar 18, 2019 at 3:04 PM Russell King - ARM Linux admin
<linux@armlinux.org.uk> wrote:
> On Mon, Mar 18, 2019 at 09:30:53AM +0100, Linus Walleij wrote:
> > This adds support for setting the flag bit "write allocate
> > override" to the L210 variant.
> >
> > The "write allocate override" bit is used on the Nomadik STn8815
> > and is necessary to properly make use of the L210 cache on that
> > machine without sporadic crashes.
> >
> > After this the platform can boot and run without any out-of-tree
> > patches.
>
> This is not something that should be done by the kernel but by the
> firmware - needing this bit set is a basic requirement of having
> the caches enabled, and if (eg) the boot loader enables the caches
> it too will suffer this problem.

I see your point. This U-Boot port does not enable the cache, I guess
because it was a bit unusual for ARM926EJ-S machines to have
L2 cache at  the time, and I remember U-Boot was not using L2CC for
a long time (maybe still not?).

The Nomadik was unstable for years and then I looked at the
outoftree vendor kernel and saw that it sets this bit and since I did that
it has been rock solid.

I can of course try to recompile and reflash the U-Boot for this
board but it is stored in NAND flash and if I break it, ugh, I have
toasted this board and I only have one. So I'm scared about that.

I have been carrying this as an out-of-tree patch for years and I can of
course continue to do so, I just felt it was a bit sad so I tried
to diet down the previous patch to the single bit the Nomadik
needs to set up for it's L2CC to work.

Yours,
Linus Walleij