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Date:   Fri, 06 Jul 2018 10:00:47 -0700
From:   pheragu@codeaurora.org
To:     Joe Perches <joe@perches.com>
Cc:     Mark Rutland <mark.rutland@arm.com>, apw@canonical.com,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        linux-kernel@vger.kernel.org, ckadabi@codeaurora.org,
        tsoni@codeaurora.org, bryanh@codeaurora.org
Subject: Re: [PATCH] checkpatch: Add exceptions for dsb keyword usage
In-Reply-To: <ebc3e5cafdf2a11a08940357c91b8ce64e7d3200.camel@perches.com>
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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.