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Date:   Thu, 7 Oct 2021 07:37:39 +0900
From:   Stafford Horne <shorne@gmail.com>
To:     Segher Boessenkool <segher@kernel.crashing.org>
Cc:     Rob Herring <robh@kernel.org>, Rich Felker <dalias@libc.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
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        "H. Peter Anvin" <hpa@zytor.com>, linux-riscv@lists.infradead.org,
        Will Deacon <will@kernel.org>, Jonas Bonn <jonas@southpole.se>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Yoshinori Sato <ysato@users.osdn.me>, linux-sh@vger.kernel.org,
        x86@kernel.org, Russell King <linux@armlinux.org.uk>,
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Subject: Re: [PATCH 06/12] openrisc: Use of_get_cpu_hwid()
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Hi Segher,

On Wed, Oct 06, 2021 at 04:27:28PM -0500, Segher Boessenkool wrote:
> On Thu, Oct 07, 2021 at 05:44:00AM +0900, Stafford Horne wrote:
> > You have defined of_get_cpu_hwid to return u64, will this create compiler
> > warnings when since we are storing a u64 into a u32?
> > 
> > It seems only if we make with W=3.
> 
> Yes.  This is done by -Wconversion, "Warn for implicit conversions that
> may alter a value."

Yeah, that is what I found out when I looked into it.

> > I thought we usually warned on this.
> 
> This warning is not in -Wall or -Wextra either, it suffers too much from
> false positives.  It is very natural to just ignore the high bits of
> modulo types (which is what "unsigned" types *are*).  Or the bits that
> "fall off" on a conversion.  The C standard makes this required
> behaviour, it is useful, and it is the only convenient way of getting
> this!

Thanks for the background, It does make sense. I guess I was confused with java
which requires casting when you store to a smaller size.  I.e.

    Test.java:5: error: incompatible types: possible lossy conversion from int to short
	s = i;

-Stafford