linux-kernel - Re: [PATCH 1/6] MIPS: remove cpu_has_64bit_gp_regs and cpu_has_64bit

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Message-ID: <20200325095435.GA27807@lst.de>
Date:   Wed, 25 Mar 2020 10:54:35 +0100
From:   Christoph Hellwig <hch@....de>
To:     Fredrik Noring <noring@...rew.org>
Cc:     Christoph Hellwig <hch@....de>,
        "Maciej W. Rozycki" <macro@...ux-mips.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/6] MIPS: remove cpu_has_64bit_gp_regs and
 cpu_has_64bit_addresses

On Wed, Mar 25, 2020 at 10:24:46AM +0100, Fredrik Noring wrote:
> > > The (slightly outdated) patch series under review
> > > is available here:
> > > 
> > > https://lore.kernel.org/linux-mips/cover.1567326213.git.noring@nocrew.org/T/
> > 
> > You don't happen to have a git tree available somewhere?
> 
> https://github.com/frno7/linux/tree/ps2-v5.4
> 
> is stable at v5.4,
> 
> https://github.com/frno7/linux/tree/ps2-master
> 
> has more experimental stuff (also at v5.4 at the moment). There are some
> (work-in-progress) notes on the R5900 psABI, that may be of interest, here:
> 
> https://github.com/frno7/linux/wiki/R5900-processor-specific-ABI-(psABI)

So from what I can tell this uses a 32-bit kernel and 32-bit userspace,
and sets both pu_has_64bit_gp_regs and cpu_has_64bit_addresses to 0.

Now if you ever wanted to make use of the 64-bit registeres it would
require quite some changes, which probably really should have a new
Kconfig option.  In fact a lot of the workaround for the 64-bit
registeres that are in the code already should be keyed off such an
option rather than CONFIG_CPU_R5900.