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From: Suzuki K Poulose <suzuki.poulose@arm.com>
To: andrew.murray@arm.com, mathieu.poirier@linaro.org,
	alexander.shishkin@linux.intel.com
Cc: Al.Grant@arm.com, coresight@lists.linaro.org, leo.yan@linaro.org,
	Sudeep.Holla@arm.com, linux-arm-kernel@lists.infradead.org,
	mike.leach@linaro.org
Subject: Re: [PATCH v4 6/6] dt-bindings: arm: coresight: Add support for coresight-needs-save-restore
Date: Fri, 2 Aug 2019 11:40:54 +0100
Message-ID: <9df0eea2-a9bd-3a93-ca51-9c3d2391a1cf@arm.com> (raw)
In-Reply-To: <20190730125157.884-7-andrew.murray@arm.com>

Hi Andrew,

On 30/07/2019 13:51, Andrew Murray wrote:
> Some coresight components, because of choices made during hardware
> integration, require their state to be saved and restored across CPU low
> power states.
> 
> The software has no reliable method of detecting when save/restore is
> required thus let's add a binding to inform the kernel.
> 
> Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> ---
>   Documentation/devicetree/bindings/arm/coresight.txt | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/arm/coresight.txt b/Documentation/devicetree/bindings/arm/coresight.txt
> index fcc3bacfd8bc..7cbdb7893af8 100644
> --- a/Documentation/devicetree/bindings/arm/coresight.txt
> +++ b/Documentation/devicetree/bindings/arm/coresight.txt
> @@ -92,6 +92,9 @@ its hardware characteristcs.
>   	* arm,cp14: must be present if the system accesses ETM/PTM management
>   	  registers via co-processor 14.
>   
> +	* arm,coresight-needs-save-restore: boolean. Indicates that software
> +	  should save/restore state across power down.
> +

Do you think we could be a bit more descriptive here about when people could add
it to the DT ? Here we don't mention when someone should use this property and
it may be added to platforms where it may be absolutely unnecessary. How about :

"Indicates that the hardware implementation may not honor the Powerup request
from the software and thus might loose the register context on CPU power down 
(e.g, during CPUIdle). Software must save/restore the context during a CPU power 
transition cycle."

Cheers
Suzuki

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Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-30 12:51 [PATCH v4 0/6] coresight: etm4x: save/restore ETMv4 context across CPU low power states Andrew Murray
2019-07-30 12:51 ` [PATCH v4 1/6] coresight: etm4x: remove superfluous setting of os_unlock Andrew Murray
2019-07-30 12:51 ` [PATCH v4 2/6] coresight: etm4x: use explicit barriers on enable/disable Andrew Murray
2019-08-01 13:31   ` Sasha Levin
2019-08-01 14:48     ` Mathieu Poirier
2019-08-02 18:08   ` Sasha Levin
2019-07-30 12:51 ` [PATCH v4 3/6] coresight: etm4x: use module_param instead of module_param_named Andrew Murray
2019-08-02 10:23   ` Suzuki K Poulose
2019-07-30 12:51 ` [PATCH v4 4/6] coresight: etm4x: improve clarity of etm4_os_unlock comment Andrew Murray
2019-07-30 12:51 ` [PATCH v4 5/6] coresight: etm4x: save/restore state across CPU low power states Andrew Murray
2019-07-30 21:16   ` Mathieu Poirier
2019-07-30 21:45     ` Andrew Murray
2019-07-31  8:16       ` Mike Leach
2019-07-31  9:45         ` Andrew Murray
2019-08-02 10:54   ` Suzuki K Poulose
2019-08-14  9:12     ` Andrew Murray
2019-07-30 12:51 ` [PATCH v4 6/6] dt-bindings: arm: coresight: Add support for coresight-needs-save-restore Andrew Murray
2019-08-02 10:40   ` Suzuki K Poulose [this message]
2019-08-02 14:37     ` Andrew Murray
2019-08-04 13:13       ` Mathieu Poirier
2019-08-14 10:01         ` Andrew Murray
2019-08-14 11:06           ` Mike Leach
2019-08-14 12:35             ` Suzuki K Poulose
2019-08-14 12:49               ` Andrew Murray
2019-08-14 14:20               ` Mike Leach
2019-07-30 20:12 ` [PATCH v4 0/6] coresight: etm4x: save/restore ETMv4 context across CPU low power states Mathieu Poirier
2019-07-30 21:46   ` Andrew Murray

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