linux-kernel - Re: [PATCH v2] riscv: keep 32-bit kernel to 32-bit phys_addr

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Message-ID: <mhng-d39bd2da-7e27-484a-b8f8-a96edf1336c0@palmerdabbelt-glaptop>
Date:   Fri, 10 Jan 2020 13:24:18 -0800 (PST)
From:   Palmer Dabbelt <palmerdabbelt@...gle.com>
To:     Olof Johansson <olof@...om.net>
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Olof Johansson <olof@...om.net>
Subject:     Re: [PATCH v2] riscv: keep 32-bit kernel to 32-bit phys_addr_t

On Mon, 06 Jan 2020 15:20:24 PST (-0800), Olof Johansson wrote:
> While rv32 technically has 34-bit physical addresses, no current platforms
> use it and it's likely to shake out driver bugs.
>
> Let's keep 64-bit phys_addr_t off on 32-bit builds until one shows up,
> since other work will be needed to make such a system useful anyway.
>
> PHYS_ADDR_T_64BIT is def_bool 64BIT, so just remove the select.
>
> Signed-off-by: Olof Johansson <olof@...om.net>
> ---
>
> v2: Just remove the select, since it's set by default if CONFIG_64BIT
>
>  arch/riscv/Kconfig | 2 --
>  1 file changed, 2 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index a31169b02ec06..569fc6deb94d6 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -12,8 +12,6 @@ config 32BIT
>
>  config RISCV
>  	def_bool y
> -	# even on 32-bit, physical (and DMA) addresses are > 32-bits
> -	select PHYS_ADDR_T_64BIT
>  	select OF
>  	select OF_EARLY_FLATTREE
>  	select OF_IRQ

I gave 5.5-rc5 a quick test on a 32-bit QEMU with 8GiB of RAM and the system
wouldn't boot, so we've got at least some bugs floating around somewhere.
Given that this doesn't work I don't see any reason to keep it around as an
option, as if someone wants to make it work there's a lot more to do than make
things compile.

I've put this on for-next.  If anyone cares about 34-bit physical addresses on
rv32 then now is the right time to speak up... ideally by fixing it :)

Thanks!