Re: [PATCH v4 03/14] coresight: move shared barrier_pkt[] to coresight_priv.h

[Greg Kroah-Hartman]

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@xxxxxxxxxx>
> Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: Suzuki K Poulose <Suzuki.Poulose@xxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> Signed-off-by: Kim Phillips <kim.phillips@xxxxxxx>
> ---
>  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