linux-kernel - Re: [RESEND PATCH V3 2/2] riscv: add RISC-V Svpbmt extension supports

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Date:   Tue, 2 Nov 2021 07:07:34 +0100
From:   Christoph Hellwig <hch@....de>
To:     Wei Fu <wefu@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Anup Patel <anup.patel@....com>,
        Atish Patra <atish.patra@....com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>, guoren@...nel.org,
        christoph.muellner@...ll.eu,
        Philipp Tomsich <philipp.tomsich@...ll.eu>,
        Christoph Hellwig <hch@....de>,
        Liu Shaohua <liush@...winnertech.com>,
        Wei Wu (吴伟) <lazyparser@...il.com>,
        Drew Fustini <drew@...gleboard.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        taiten.peng@...onical.com, aniket.ponkshe@...onical.com,
        heinrich.schuchardt@...onical.com, gordan.markus@...onical.com,
        guoren@...ux.alibaba.com, Arnd Bergmann <arnd@...db.de>,
        Chen-Yu Tsai <wens@...e.org>,
        Maxime Ripard <maxime@...no.tech>,
        Daniel Lustig <dlustig@...dia.com>,
        Greg Favor <gfavor@...tanamicro.com>,
        Andrea Mondelli <andrea.mondelli@...wei.com>,
        Jonathan Behrens <behrensj@....edu>,
        Xinhaoqu <xinhaoqu@...wei.com>,
        Bill Huffman <huffman@...ence.com>,
        Nick Kossifidis <mick@....forth.gr>,
        Allen Baum <allen.baum@...erantotech.com>,
        Josh Scheid <jscheid@...tanamicro.com>,
        Richard Trauben <rtrauben@...il.com>
Subject: Re: [RESEND PATCH V3 2/2] riscv: add RISC-V Svpbmt extension
 supports

On Mon, Oct 25, 2021 at 06:55:09PM +0800, Wei Fu wrote:
> How about this macro:
> #define _SVPBMT_PMA         0x0UL
> #define _SVPBMT_NC         BIT(61)
> #define _SVPBMT_IO         BIT(62)
> #define _SVPBMT_MASK         GENMASK(62, 61)

Personally I find these macros highly confusing. 

#define _SVPBMT_PMA	0UL
#define _SVPBMT_NC	(1UL << 61)
#define _SVPBMT_IO	(1UL << 62).
#define _SVPBMT_MASK	(_SVPBMT_NC  | _SVPBMT_IO)

is much eaier to follow.  Note that we can probably just drop
_SVPBMT_PMA entirely to make this even more readable.

> > Also why not use the standard names for these _PAGE bits used by
> > most other architectures?
> 
> Which names are you suggesting? Would you mind providing an example ?
> _PAGE_BIT_   for _PAGE_KERNEL_ ??

Use _PAGE_NOCACHE for _SVPBMT_NC, and _PAGE_IO for _SVPBMT_IO.