Subject: [PATCH] coresight: STM: Balance enable/disable

From: [email-masked] (Greg KH)
Date: Thu, 19 Jan 2017 12:40:37 +0100

On Mon, Jan 16, 2017 at 06:00:00PM +0000, Suzuki K Poulose wrote:
> The stm is automatically enabled when an application sets the policy
> via ->link() call back by using coresight_enable(), which keeps the
> refcount of the current users of the STM. However, the unlink() callback
> issues stm_disable() directly, which leaves the STM turned off, without
> the coresight layer knowing about it. This prevents any further uses
> of the STM hardware as the coresight layer still thinks the STM is
> turned on and doesn't enable the hardware when required. Even manually
> enabling the STM via sysfs can't really enable the hw.
> 
> e.g,
> 
>  $ echo 1 > $CS_DEVS/$ETR/enable_sink
>  $ mkdir -p $CONFIG_FS/stp-policy/$source.0/stm_test/
>  $ echo 32768 65535 > $CONFIG_FS/stp-policy/$source.0/stm_test/channels
>  $ echo 64 > $CS_DEVS/$source/traceid
>  $ ./stm_app
>  Sending 64000 byte blocks of pattern 0 at 0us intervals
>  Success to map channel(32768~32783) to 0xffffa95fa000
>  Sending on channel 32768
>  $ dd if=/dev/$ETR of=~/trace.bin.1
>  597+1 records in
>  597+1 records out
>  305920 bytes (306 kB) copied, 0.399952 s, 765 kB/s
>  $ ./stm_app
>  Sending 64000 byte blocks of pattern 0 at 0us intervals
>  Success to map channel(32768~32783) to 0xffff7e9e2000
>  Sending on channel 32768
>  $ dd if=/dev/$ETR of=~/trace.bin.2
>  0+0 records in
>  0+0 records out
>  0 bytes (0 B) copied, 0.0232083 s, 0.0 kB/s
> 
>  Note that we don't get any data from the ETR for the second session.
> 
>  Also dmesg shows :
> 
>  [   77.520458] coresight-tmc 20800000.etr: TMC-ETR enabled
>  [   77.537097] coresight-replicator etr_replicator at 20890000: REPLICATOR enabled
>  [   77.558828] coresight-replicator main_replicator at 208a0000: REPLICATOR enabled
>  [   77.581068] coresight-funnel 208c0000.main_funnel: FUNNEL inport 0 enabled
>  [   77.602217] coresight-tmc 20840000.etf: TMC-ETF enabled
>  [   77.618422] coresight-stm 20860000.stm: STM tracing enabled
>  [  139.554252] coresight-stm 20860000.stm: STM tracing disabled
>   # End of first tracing session
>  [  146.351135] coresight-tmc 20800000.etr: TMC read start
>  [  146.514486] coresight-tmc 20800000.etr: TMC read end
>   # Note that the STM is not turned on via stm_generic_link()->coresight_enable()
>   # and hence none of the components are turned on.
>  [  152.479080] coresight-tmc 20800000.etr: TMC read start
>  [  152.542632] coresight-tmc 20800000.etr: TMC read end
> 
> This patch fixes the problem by balancing the unlink operation by using
> the coresight_disable(), keeping the coresight layer in sync with the
> hardware state and thus allowing normal usage of the STM component.
> 
> Fixes: commit 237483aa5cf43 ("coresight: stm: adding driver for CoreSight STM component")
> Cc: Pratik Patel <[email-masked]>
> Cc: Greg Kroah-Hartman <[email-masked]>
> Cc: stable at vger.kernel.org # 4.7+
> Acked-by: Mathieu Poirier <[email-masked]>
> Reviewed-by: Chunyan Zhang <[email-masked]>
> Reported-by: Robert Walker <[email-masked]>
> Signed-off-by: Suzuki K Poulose <[email-masked]>
> ---
> 
> Greg,
> 
> Without this patch, the coresight STM IP can only be used for one tracing
> session per boot, seriously limiting its usability.

When you resend a patch, please tell me what is different from the
previous version you sent.  I figured it out here, but please do this
next time.

thanks,

greg k-h