linux-kernel - Re: [PATCH v4 12/21] arm64: cpufeature: Add an early command-line cpufeature override facility

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Message-ID: <87v9bmjof8.wl-maz@kernel.org>
Date:   Sun, 24 Jan 2021 16:21:47 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        David Brazdil <dbrazdil@...gle.com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Jing Zhang <jingzhangos@...gle.com>,
        Ajay Patil <pajay@....qualcomm.com>,
        Prasad Sodagudi <psodagud@...eaurora.org>,
        Srinivas Ramana <sramana@...eaurora.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        kernel-team@...roid.com
Subject: Re: [PATCH v4 12/21] arm64: cpufeature: Add an early command-line cpufeature override facility

On Sat, 23 Jan 2021 13:43:52 +0000,
Catalin Marinas <catalin.marinas@....com> wrote:
> 
> On Mon, Jan 18, 2021 at 09:45:24AM +0000, Marc Zyngier wrote:
> > +struct reg_desc {
> > +	const char * const	name;
> > +	u64 * const		val;
> > +	u64 * const		mask;
> > +	struct {
> > +		const char * const	name;
> > +		u8			 shift;
> > +	} 			fields[];
> > +};
> 
> Sorry, I didn't see this earlier. Do we need to add all these consts
> here? So you want the pointers to be const but why is 'shift' special
> and not a const then? Is it modified later?
> 
> Would this not work:
> 
> struct reg_desc {
> 	const char	*name;
> 	u64		*val;
> 	u64		*mask;
> 	struct {
> 		const char	*name;
> 		u8		shift;
> 	} fields[];
> };
> 
> > +static const struct reg_desc * const regs[] __initdata = {
> 
> as we already declare the whole struct reg_desc pointers here as const.
> I may have confused myself...

It definitely is better. Specially given that we throw all of this
away right after boot, there is no harm in keeping it simple.

I've also renamed "reg_desc" to "ftr_set_desc", because we don't
always describe a register (like for kaslr).

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.