linux-kernel - Re: [PATCH v1 4/9] scsi: ufs: add option to change default UFS power management level

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Date:   Mon, 23 Jul 2018 08:50:40 +0530
From:   "Asutosh Das (asd)" <asutoshd@...eaurora.org>
To:     Rob Herring <robh@...nel.org>
Cc:     subhashj@...eaurora.org, cang@...eaurora.org,
        vivek.gautam@...eaurora.org, rnayak@...eaurora.org,
        vinholikatti@...il.com, jejb@...ux.vnet.ibm.com,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Venkat Gopalakrishnan <venkatg@...eaurora.org>,
        Mark Rutland <mark.rutland@....com>,
        Mathieu Malaterre <malat@...ian.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 4/9] scsi: ufs: add option to change default UFS power
 management level

On 7/12/2018 2:03 AM, Rob Herring wrote:
> On Fri, Jul 06, 2018 at 06:00:31PM +0530, Asutosh Das wrote:
>> From: Subhash Jadavani <subhashj@...eaurora.org>
>>
>> UFS device and link can be put in multiple different low power modes hence
>> UFS driver supports multiple different low power modes. By default UFS
>> driver selects the default (optimal) low power mode (which gives moderate
>> power savings and have relatively less enter and exit latencies) but
>> we might have to tune this default power mode for different chipset
>> platforms to meet the low power requirements/goals. Hence this patch
>> adds option to change default UFS low power mode (level).
>>
>> Signed-off-by: Subhash Jadavani <subhashj@...eaurora.org>
>> Signed-off-by: Venkat Gopalakrishnan <venkatg@...eaurora.org>
>> Signed-off-by: Can Guo <cang@...eaurora.org>
>> Signed-off-by: Asutosh Das <asutoshd@...eaurora.org>
>> ---
>>   .../devicetree/bindings/ufs/ufshcd-pltfrm.txt      | 11 ++++++++
>>   drivers/scsi/ufs/ufshcd-pltfrm.c                   | 14 +++++++++++
>>   drivers/scsi/ufs/ufshcd.c                          | 29 +++++++++++++++-------
>>   drivers/scsi/ufs/ufshcd.h                          |  4 +--
>>   4 files changed, 47 insertions(+), 11 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt b/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
>> index c39dfef..f564d9a 100644
>> --- a/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
>> +++ b/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
>> @@ -38,6 +38,15 @@ Optional properties:
>>   			  defined or a value in the array is "0" then it is assumed
>>   			  that the frequency is set by the parent clock or a
>>   			  fixed rate clock source.
>> +- rpm-level		: UFS Runtime power management level. Following PM levels are supported:
>> +			  0 - Both UFS device and Link in active state (Highest power consumption)
>> +			  1 - UFS device in active state but Link in Hibern8 state
>> +			  2 - UFS device in Sleep state but Link in active state
>> +			  3 - UFS device in Sleep state and Link in hibern8 state (default PM level)
>> +			  4 - UFS device in Power-down state and Link in Hibern8 state
>> +			  5 - UFS device in Power-down state and Link in OFF state (Lowest power consumption)
>> +- spm-level		: UFS System power management level. Allowed PM levels are same as rpm-level.
> 
> What's the default?
> 
> I assume these are minimums? The OS can pick higher power states. This
> seems to be a bit Linux specific (as 'runtime PM' could be considered
> Linux specific). For every other device, we don't put this type of
> information in DT, but is user controlled.
I didn't completely understand your comment.
Do you not want these properties to be in DT file?
When you say user-controlled, do you mean control it through sysfs entries?

> So really, wouldn't 1
> property be sufficient for cases where a mode doesn't work due to
> some h/w limitation. Otherwise, it is an OS or user decision.
I didn't completely understand this. Could you please elaborate on your 
intent here?

> 
>> +
>>   -lanes-per-direction	: number of lanes available per direction - either 1 or 2.
>>   			  Note that it is assume same number of lanes is used both
>>   			  directions at once. If not specified, default is 2 lanes per direction.
>> @@ -66,4 +75,6 @@ Example:
>>   		freq-table-hz = <100000000 200000000>, <0 0>, <0 0>;
>>   		phys = <&ufsphy1>;
>>   		phy-names = "ufsphy";
>> +		rpm-level = <3>;
> 
> Why specified if 3 is the default?
Ah yes - that should be removed.
I'll remove it in v2.

> 
>> +		spm-level = <5>;
> 
> These seem like sane defaults. When and why would you use some
> different?
I think each of the deeper sleep modes are associated with an increasing 
wakeup latency. For e.g. '0' would have the highest power-consumption 
and no resume latency at all as compared to '5'.
So depending on use-cases other modes may be chosen.

> 
> Rob
> 

-asd

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