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SubjectRe: [PATCH] checkpatch: Add exceptions for dsb keyword usage
On 2018-07-05 22:52, Joe Perches wrote:
> On Fri, 2018-07-06 at 06:45 +0100, Mark Rutland wrote:
>> On Thu, Jul 05, 2018 at 02:14:28PM -0700, Joe Perches wrote:
>> > On Thu, 2018-07-05 at 11:19 -0700, Prakruthi Deepak Heragu wrote:
>> > > mb() API can relpace the dsb() API in the kernel code. So, dsb() usage
>> > > is discouraged. However, there are exceptions when dsb is used in a
>> > > variable or a function name. Exceptions are when 'dsb' is prefixed with
>> > > class [-_>*\.] and/or suffixed with class [-_\.;].
>>
>> This is a really confusing way of describing the match behaviour, and
>> doesn't
>> explain why this is a big problem.
>>
>> In C it's either:
>>
>> dsb()
>> dsb(scope) // e.g. dsb(ish)
>>
>> ... where scope is [a-z]*.
>>
>> ... which can be matched as something like 'dsb([a-z]*)' if necessary.
>>
>> > []
>> > > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
>> >
>> > []
>> > > @@ -5372,6 +5372,12 @@ sub process {
>> > > "Avoid line continuations in quoted strings\n" . $herecurr);
>> > > }
>> > >
>> > > +# dsb is too ARMish, and should usually be mb.
>> > > + if ($line =~ /[^-_>*\.]\bdsb\b[^-_\.;]/) {
>> > > + WARN("ARM_BARRIER",
>> > > + "Use of dsb is discouranged: prefer mb.\n" .
>> > > + $herecurr);
>> > > + }
>> >
>> > This patch is whitespace damaged with a spelling error.
>> >
>> > Also, if this is reasonable test, and I don't know
>> > that it is, it should be cc'd to the linux-arm list
>> > linux-arm-kernel@lists.infradead.org
>> >
>> > Also, I suggest 2 tests, one for .S files and
>> > another for .[ch] files, and this be made specific
>> > to arch/arm... files
>> >
>> > Something like:
>> >
>> > if ($realfile =~ @^arch/arm@ &&
>> > ($realfile =~ /\.S$/ && $line =~ /\bdsb\b/) ||
>> > ($realfile =~ /\.[ch]$/ && $line =~ /\bdsb\s*\(/)) {
>> > WARN("ARM_DSB",
>> > "Prefer mb over dsb as an ARM memory barrier\n" . $herecurr);
>> > }
>> >
>> > ARM people, is this reasonable?
>>
>> I don't think this is a big deal today.
>>
>> For code under arch/{arm,arm64}, it's perfectly reasonable to use dsb.
>>
>> For code *ouside* of arch/{arm,arm64}, there are a number of cases
>> where we
>> want to use dsb(), e.g. when dealing with architectural drivers that
>> require
>> special barriers, or for common code shared across arm and arm64.
>>
>> It doesn't look like this is a big problem today, anyhow:
>>
>> [mark@salmiak:~/src/linux]% git grep -w 'dsb(.*)' -- ^arch
>> drivers/irqchip/irq-armada-370-xp.c: dsb();
>> drivers/irqchip/irq-gic-v3-its.c: dsb(ishst);
>> drivers/irqchip/irq-gic-v3-its.c: dsb(ishst);
>> drivers/irqchip/irq-gic-v3-its.c: dsb(sy);
>> drivers/irqchip/irq-gic-v3-its.c: dsb(sy);
>> drivers/irqchip/irq-gic-v3-its.c: dsb(sy);
>> drivers/mtd/nand/raw/cmx270_nand.c: dsb();
>> drivers/mtd/nand/raw/cmx270_nand.c: dsb();
>> drivers/mtd/nand/raw/cmx270_nand.c: dsb();
>> drivers/mtd/nand/raw/cmx270_nand.c: dsb();
>> drivers/mtd/nand/raw/cmx270_nand.c: dsb();
>> drivers/perf/arm_spe_pmu.c: dsb(nsh);
>> drivers/perf/arm_spe_pmu.c: dsb(nsh);
>> drivers/power/reset/arm-versatile-reboot.c: dsb();
>> drivers/soc/rockchip/pm_domains.c: dsb(sy);
>> drivers/soc/rockchip/pm_domains.c: dsb(sy);
>> drivers/staging/mt7621-mmc/sd.c: //dsb(); /* --- by chhung */
>> drivers/staging/mt7621-mmc/sd.c: //dsb(); /* --- by chhung */
>> drivers/staging/vc04_services/interface/vchiq_arm/vchiq.h:#define
>> dsb(a)
>> drivers/staging/vc04_services/interface/vchiq_arm/vchiq_2835_arm.c:
>> dsb(sy); /* data barrier operation */
>> drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c:
>> dsb(sy);
>> drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h: do {
>> debug_ptr[DEBUG_ ## d] = __LINE__; dsb(sy); } while (0)
>> drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h: do {
>> debug_ptr[DEBUG_ ## d] = (v); dsb(sy); } while (0)
>> drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h: do {
>> debug_ptr[DEBUG_ ## d]++; dsb(sy); } while (0)
>> virt/kvm/arm/hyp/vgic-v3-sr.c: dsb(sy);
>> virt/kvm/arm/hyp/vgic-v3-sr.c: dsb(sy);
>> virt/kvm/arm/hyp/vgic-v3-sr.c: dsb(sy);
>
> Thanks Mark.
>
> So it seems this shouldn't be applied.
Thanks Joe. I appreciate your feedback.

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