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SubjectRe: [PATCH v1 07/12] scsi: ufs: add option to change default UFS power management level
On 2016-12-13 12:04, Rob Herring wrote:
> On Mon, Dec 12, 2016 at 04:54:20PM -0800, Subhash Jadavani wrote:
>> 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).
>>
>> Reviewed-by: Yaniv Gardi <ygardi@codeaurora.org>
>> Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
>> ---
>> .../devicetree/bindings/ufs/ufshcd-pltfrm.txt | 10 ++++++
>> drivers/scsi/ufs/ufshcd-pltfrm.c | 14 ++++++++
>> drivers/scsi/ufs/ufshcd.c | 39
>> ++++++++++++++++++++++
>> drivers/scsi/ufs/ufshcd.h | 4 +--
>> 4 files changed, 65 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
>> b/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
>> index a99ed55..c3836c5 100644
>> --- a/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
>> +++ b/Documentation/devicetree/bindings/ufs/ufshcd-pltfrm.txt
>> @@ -41,6 +41,14 @@ Optional properties:
>> -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.
>> +- 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.
>
> This looks like you are putting policy for Linux into DT.
>
> What I would expect to see here is disabling of states that don't work
> due to some h/w limitation. Otherwise, it is a user decision for what
> modes to go into. Also, I think link and device states should be
> separate.

Yes, generally default level (3) is good enough (and recommended) for
all platforms and most likely user is only expected to change this if
they see issues (most H/W) on their platform or they want even more
aggressive power state (level-4 or level-5) and ready to take the
performance hit associated with resume latencies.

Also, I think it is better to keep Link and device states tied, one
reason is that we can't keep device in sleep/active state when Link is
in OFF state.

>
> Rob

--
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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