linux-kernel - Re: [PATCH] mips: Realtek RTL: select NO_EXCEPT

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Date:   Fri, 17 Feb 2023 18:37:08 +0100
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Olliver Schinagl <oliver@...inagl.nl>
Cc:     Sander Vanheule <sander@...nheule.net>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mips: Realtek RTL: select NO_EXCEPT_FILL

On Sun, Feb 05, 2023 at 07:33:46PM +0100, Olliver Schinagl wrote:
> > I always thought that SWAP_IO_SPACE is needed for big endian, but
> > looking at arch/mips/Kconfig I see a lot of SWAP_IO_SPACE for pure
> > little endian machines. I need to dig deeper to understand why.
> Thank you!

and the reason why this works is simple, CONFIG_SWAP_IO_SPACE is a nop
for little endian.

> > such a change would defeat the generic part of GENERIC_MIPS_KERNEL,
> > because it will then only work on REALTEC_SOC and nothing else.
> Ignoring the potential incorrect detail here, obviously I would prefer to
> use the GENERIC_MIPS_KERNEL, but having to copy the whole config just to
> leave out that one option also is kinda meh. So i'm hoping we can find a
> solution of course :)

what SOC is this exactly ? Do you have a programmers manual for it,
which contains details about the PCI bridge ? Most of the PCI bridges
used for MIPS contain a bit to select the endianess of the access
to PCI spaces. If there is such a config just changing the current
setting, should solve your problem.

If this isn't possible you could use something similair to the
INGENIC approach, which could use a generic kernel but also an
customized kernel. And in such a customized kernel it should be
possible to remove SWAP_IO_SPACE.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]