linux-kernel - Re: [PATCH v4 03/14] coresight: move shared barrier_pkt[] to coresight

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Date:   Wed, 6 Jun 2018 10:27:57 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Kim Phillips <kim.phillips@....com>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Suzuki K Poulose <Suzuki.Poulose@....com>,
        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 v4 03/14] coresight: move shared barrier_pkt[] to
 coresight_priv.h

On Tue, Jun 05, 2018 at 04:06:59PM -0500, Kim Phillips wrote:
> barrier_pkt[] is used in the etb and tmc-etf coresight
> components.  Change barrier_pkt[] to a static definition,
> so as to allow them to be built as modules.
> 
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Leo Yan <leo.yan@...aro.org>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Randy Dunlap <rdunlap@...radead.org>
> Cc: Suzuki K Poulose <Suzuki.Poulose@....com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Russell King <linux@...linux.org.uk>
> Signed-off-by: Kim Phillips <kim.phillips@....com>
> ---
>  drivers/hwtracing/coresight/coresight-priv.h | 8 +++++++-
>  drivers/hwtracing/coresight/coresight.c      | 7 -------
>  2 files changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
> index 158c720119dd..e76f19ca9e04 100644
> --- a/drivers/hwtracing/coresight/coresight-priv.h
> +++ b/drivers/hwtracing/coresight/coresight-priv.h
> @@ -57,7 +57,13 @@ static DEVICE_ATTR_RO(name)
>  #define coresight_simple_reg64(type, name, lo_off, hi_off)		\
>  	__coresight_simple_func(type, NULL, name, lo_off, hi_off)
>  
> -extern const u32 barrier_pkt[4];
> +/*
> + * When losing synchronisation a new barrier packet needs to be inserted at the
> + * beginning of the data collected in a buffer.  That way the decoder knows that
> + * it needs to look for another sync sequence.
> + */
> +static const u32 barrier_pkt[4] = { 0x7fffffff, 0x7fffffff,
> +				    0x7fffffff, 0x7fffffff };

Are you _sure_ this is doing what you think it is doing?

You now just created a bunch of different copies of this structure,
which might change the logic involved, right?

Putting a static variable in a .h file is generally considered a very
bad thing to do, I need a lot more "proof" this is ok before I can
accept this.  Worse case, just put the variable in the individual places
where it is needed.

thanks,

greg k-h