linux-kernel - Re: [PATCH v4 0/7] firmware: smccc: Add basic SMCCC v1.2 + ARCH_SOC

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Message-ID: <CAK8P3a3cPPiprEpF_k-GWAgWSZiP3Qp3v++jvS_8W17Ns4_HGw@mail.gmail.com>
Date:   Thu, 21 May 2020 12:31:32 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Steven Price <steven.price@....com>, harb@...erecomputing.com,
        Will Deacon <will@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 0/7] firmware: smccc: Add basic SMCCC v1.2 +
 ARCH_SOC_ID support

On Thu, May 21, 2020 at 12:14 PM Russell King - ARM Linux admin
<linux@...linux.org.uk> wrote:
>
> On Thu, May 21, 2020 at 11:06:23AM +0200, Arnd Bergmann wrote:
> > Note that the warning should come up for either W=1 or C=1, and I also
> > think that
> > new code should generally be written sparse-clean and have no warnings with
> > 'make C=1' as a rule.
>
> No, absolutely not, that's a stupid idea, there are corner cases
> where hiding a sparse warning is the wrong thing to do.  Look at
> many of the cases in fs/ for example.
>
> See https://lkml.org/lkml/2004/9/12/249 which should make anyone
> who sees a use of __force in some random code stop and question
> why it is there, and whether it is actually correct, or just there
> to hide a sparse warning.
>
> Remember, sparse is there to warn that something isn't quite right,
> and the view taken is, if it isn't right, then we don't "cast the
> warning away" with __force, even if we intend not to fix the code
> immediately.
>
> So, going for "sparse-clean" is actually not correct. Going for
> "no unnecessary warnings" is.
>
> And don't think what I've said above doesn't happen; I've rejected
> patches from people who've gone around trying to fix every sparse
> warning that they see by throwing __force incorrectly at it.
>
> The thing is, if you hide all the warnings, even for incorrect code,
> then sparse becomes completely useless to identify where things in
> the code are not quite correct.

Adding __force is almost always the wrong solution, and I explictly
was not talking about existing code here where changing it would
risk introducing bugs or require bad hacks.

However, when writing a new driver, sparse warnings usually
indicate that you are doing something wrong that is better addressed
by doing something different that does not involve adding __force.

      Arnd