linux-kernel - Re: [PATCH 1/6] coresight: remove CORESIGHT_LINKS_AND

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Message-Id: <20180524183027.dc498058344604e2d6027eff@arm.com>
Date:   Thu, 24 May 2018 18:30:27 -0500
From:   Kim Phillips <kim.phillips@....com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Gargi Sharma <gs051095@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Rik van Riel <riel@...hat.com>,
        Robin Murphy <robin.murphy@....com>,
        Russell King <linux@...linux.org.uk>,
        Thierry Reding <treding@...dia.com>,
        Todd Kjos <tkjos@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] coresight: remove CORESIGHT_LINKS_AND_SINKS
 dependencies and selections

On Thu, 24 May 2018 09:32:48 -0600
Mathieu Poirier <mathieu.poirier@...aro.org> wrote:

> On 23 May 2018 at 13:51, Kim Phillips <kim.phillips@....com> wrote:
> > On Tue, 22 May 2018 11:31:40 -0600
> > Mathieu Poirier <mathieu.poirier@...aro.org> wrote:
> >
> >> On Thu, May 17, 2018 at 08:20:19PM -0500, Kim Phillips wrote:
> >> > A coresight topology doesn't need to include links, i.e., a source can
> >> > be directly connected to a sink.  As such, selecting and/or depending on
> >> > LINKS_AND_SINKS is no longer needed.
> >>
> >> I'm good with this patch but now the help text for CORESIGHT_LINKS_AND_SINKS no
> >> longer match what the config does.  I see two ways to fix this:
> >
> > This patch doesn't change what the config does, it just changes what
> > other config options depend on it.
> >
> >> 1) Rework the help text.
> >
> > I don't see how, given the above.  Here's the text:
> >
> > config CORESIGHT_LINKS_AND_SINKS
> >         bool "CoreSight Link and Sink drivers"
> >         help
> >           This enables support for CoreSight link and sink drivers that are
> >           responsible for transporting and collecting the trace data
> >           respectively.  Link and sinks are dynamically aggregated with a trace
> >           entity at run time to form a complete trace path.
> >
> > What part of that becomes invalid with this patch?
> 
> Looking at the new Kconfig, what sink component depend on
> CORESIGHT_LINKS_AND_SINKS?

How does that affect the description text?  The description text
doesn't insinuate any implicit dependencies or non-.

> config CORESIGHT_LINKS

Please, not another gratuitous config name change, I've already
experienced usage regressions from the CORESIGHT_QCOM_REPLICATOR =>
CORESIGHT_DYNAMIC_REPLICATOR change:

https://patchwork.kernel.org/patch/10206023/

>          bool "CoreSight Link drivers"
>          help
>            This enables support for CoreSight link drivers that are responsible
>            for transporting trace data from source to sink.  Links are
> dynamically
>            aggregated with other traces entities at run time to form a
> complete trace
>            path.

Oh, I see, so your point is that LINKS_AND_SINKS doesn't technically
build any sink drivers?  That's completely orthogonal to removing a
dependency chain:  that just tells me the name was a poor choice in the
first place maybe?  I don't see where the Makefile may have built a
sink, but it may be before the move to drivers/hwtracing/coresight, or
some other reorganization.

> >> 2) Rework CORESIGHT_LINKS_AND_SINKS to be CORESIGHT_FUNNEL and move
> >> coresight-replicator.o under CORESIGHT_DYNAMIC_REPLICATOR in the Makefile. I
> >> really liked your idea of making the replicator driver intelligent enough to
> >> deal with both DT and platform declaration, which merges two driver into one.
> >>
> >> I'm obviously favouring the second option but recognise it doesn't have to be
> >> part of this patchet.  So for this set please rework the help text for
> >> CORESIGHT_LINKS_AND_SINKS.  Once we've dealt with this topic we can refactor the
> >> replicator driver.
> >
> > I'd really like to just focus on getting CoreSight to load as modules,
> > something for which this patch isn't technically required...
> 
> The only thing I'm asking is that the config description and help text
> reflect what the Makefile does.

argh, wellll, it's a completely different change, and we're now
completely off the modularization topic, and I'm uncomfortable doing
reorgs on things I don't understand, renaming CONFIG_s, esp. when
others such as the REPLICATOR, since as far as I know, that's also a
link??

Kim