linux-kernel - Re: [PATCH] coresight: STM: Balance enable/disable

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Message-ID: <20170119114037.GR28024@kroah.com>
Date:   Thu, 19 Jan 2017 12:40:37 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     mathieu.poirier@...aro.org, zhang.chunyan@...aro.org,
        pratikp@...eaurora.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org
Subject: Re: [PATCH] coresight: STM: Balance enable/disable

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@...90000: REPLICATOR enabled
>  [   77.558828] coresight-replicator main_replicator@...a0000: 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 <pratikp@...eaurora.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: stable@...r.kernel.org # 4.7+
> Acked-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> Reviewed-by: Chunyan Zhang <zhang.chunyan@...aro.org>
> Reported-by: Robert Walker <robert.walker@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
> 
> 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