Messages in this thread | | | From | Arnd Bergmann <> | Date | Thu, 21 May 2020 12:31:32 +0200 | Subject | Re: [PATCH v4 0/7] firmware: smccc: Add basic SMCCC v1.2 + ARCH_SOC_ID support |
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On Thu, May 21, 2020 at 12:14 PM Russell King - ARM Linux admin <linux@armlinux.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
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