linux-kernel - Re: [PATCH 1/2] coresight: etm4x: request to retain power to the trace unit when active

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Message-ID: <CANLsYkw_oMipxFaYdeS149jAHdmqJznQQob6C8NQKQ1cRYZ2YQ@mail.gmail.com>
Date:	Thu, 4 Aug 2016 11:15:08 -0600
From:	Mathieu Poirier <mathieu.poirier@...aro.org>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] coresight: etm4x: request to retain power to the
 trace unit when active

On 3 August 2016 at 10:12, Sudeep Holla <sudeep.holla@....com> wrote:
> The Coresight ETMv4 architecture provides a way to request to keep the
> power to the trace unit. This might help to collect the traces without
> the need to disable the CPU power management(entering/exiting deeper
> idle states).
>
> Trace PowerDown Control Register provides powerup request bit which when
> set requests the system to retain power to the trace unit and emulate
> the powerdown request.
>
> Typically, a trace unit drives a signal to the power controller to
> request that the trace unit core power domain is powered up. However,
> if the trace unit and the CPU are in the same power domain then the
> implementation might combine the trace unit power up status with a
> signal from the CPU.
>
> This patch requests to retain power to the trace unit when active and
> to remove when inactive. Note this change will only request but the
> behaviour depends on the implementation. However, it matches the
> exact behaviour expected when the external debugger is connected with
> respect to CPU power states.
>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  drivers/hwtracing/coresight/coresight-etm4x.c | 12 ++++++++++++
>  drivers/hwtracing/coresight/coresight-etm4x.h |  3 +++
>  2 files changed, 15 insertions(+)
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c
> index b3bde2aec2b9..c8c7829f7046 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.c
> @@ -164,6 +164,13 @@ static void etm4_enable_hw(void *info)
>         writel_relaxed(config->vmid_mask0, drvdata->base + TRCVMIDCCTLR0);
>         writel_relaxed(config->vmid_mask1, drvdata->base + TRCVMIDCCTLR1);
>
> +       /*
> +        * Request to keep the trace unit powered and also
> +        * emulation of powerdown
> +        */
> +       writel_relaxed(readl_relaxed(drvdata->base + TRCPDCR) | TRCPDCR_PU,
> +                      drvdata->base + TRCPDCR);
> +
>         /* Enable the trace unit */
>         writel_relaxed(1, drvdata->base + TRCPRGCTLR);
>
> @@ -294,6 +301,11 @@ static void etm4_disable_hw(void *info)
>
>         CS_UNLOCK(drvdata->base);
>
> +       /* power can be removed from the trace unit now */
> +       control = readl_relaxed(drvdata->base + TRCPDCR);
> +       control &= ~TRCPDCR_PU;
> +       writel_relaxed(control, drvdata->base + TRCPDCR);
> +
>         control = readl_relaxed(drvdata->base + TRCPRGCTLR);
>
>         /* EN, bit[0] Trace unit enable bit */
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> index 5359c5197c1d..2629954429a1 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -183,6 +183,9 @@
>  #define TRCSTATR_IDLE_BIT              0
>  #define ETM_DEFAULT_ADDR_COMP          0
>
> +/* PowerDown Control Register bits */
> +#define TRCPDCR_PU                     BIT(3)
> +
>  /* secure state access levels */
>  #define ETM_EXLEVEL_S_APP              BIT(8)
>  #define ETM_EXLEVEL_S_OS               BIT(9)
> --
> 2.7.4
>

Applied - thanks.
Mathieu