linux-kernel - Re: [PATCH] coresight replicator: set default y after Kconfig rename

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Message-Id: <20180208132339.349784436ca752238bb965bf@arm.com>
Date:   Thu, 8 Feb 2018 13:23:39 -0600
From:   Kim Phillips <kim.phillips@....com>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] coresight replicator: set default y after Kconfig
 rename

On Thu, 8 Feb 2018 18:01:21 +0000
Suzuki K Poulose <Suzuki.Poulose@....com> wrote:

> On 08/02/18 17:22, Kim Phillips wrote:
> > On Thu, 8 Feb 2018 08:59:30 -0700
> > Mathieu Poirier <mathieu.poirier@...aro.org> wrote:
> > 
> >> On 7 February 2018 at 14:03, Kim Phillips <kim.phillips@....com> wrote:
> >>> Commit 1c8859848dbb ("coresight replicator: Cleanup programmable
> >>> replicator naming") changed the Kconfig symbol name from
> >>> QCOM_REPLICATOR, which, whilst not in the single arm64 defconfig,
> >>> was being set in my juno build script, which left the new symbol unset,
> >>> causing the following unexpected grief:
> >>>
> >>>   # ./perf record -vvv -C 0 -e cs_etm/@...70000.etr/ --per-thread true
> >>>   ..<snip>..
> >>>   sys_perf_event_open: pid -1  cpu 0  group_fd -1  flags 0x8 = 5
> >>>   mmap size 528384B
> >>>   AUX area mmap length 4194304
> >>>   perf event ring buffer mmapped per cpu
> >>>   failed to mmap AUX area
> >>>   failed to mmap with 12 (Cannot allocate memory)
> >>>
> >>> Make it default y to help not surprise unsuspecting users.
> >>>
> >>> Fixes: 1c8859848dbb ("coresight replicator: Cleanup programmable replicator naming")
> >>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> >>> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> >>> Signed-off-by: Kim Phillips <kim.phillips@....com>
> >>> ---
> >>>   drivers/hwtracing/coresight/Kconfig | 1 +
> >>>   1 file changed, 1 insertion(+)
> >>>
> >>> diff --git a/drivers/hwtracing/coresight/Kconfig b/drivers/hwtracing/coresight/Kconfig
> >>> index ef9cb3c164e1..b94bbd95efa6 100644
> >>> --- a/drivers/hwtracing/coresight/Kconfig
> >>> +++ b/drivers/hwtracing/coresight/Kconfig
> >>> @@ -73,6 +73,7 @@ config CORESIGHT_SOURCE_ETM4X
> >>>   config CORESIGHT_DYNAMIC_REPLICATOR
> >>>          bool "CoreSight Programmable Replicator driver"
> >>>          depends on CORESIGHT_LINKS_AND_SINKS
> >>> +       default y
> >>>          help
> >>>            This enables support for dynamic CoreSight replicator link driver.
> >>>            The programmable ATB replicator allows independent filtering of the
> >>
> >> As I said before don't see why it needs to be treated differently than other CS
> >> blocks
> > 
> > I don't think it does either, but this one is special since it recently
> > underwent a rename, which breaks its users that were setting the old
> > name in their config builds.  The default y keeps it set in those
> > cases, thereby discontinuing any such regression.
> 
> I don't think the kernel CONFIG symbols are part of the kernel ABI. So,
> unfortunately the users have to take care of making sure they select what
> they need.

Right, sorry, I wan't referring to a kernel ABI regression :)  Think of
it as just trying to make Coresight easier to configure, and in this
particular case, given Coresight Kconfig symbol name volatility.

Kim