From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Asutosh Das (asd)" Subject: Re: [PATCH v1 4/9] scsi: ufs: add option to change default UFS power management level Date: Tue, 24 Jul 2018 09:04:34 +0530 Message-ID: References: <20180711203317.GA14983@rob-hp-laptop> <4b85de8b-d03e-da93-704b-e70922a9fbea@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Rob Herring Cc: Subhash Jadavani , Can Guo , Vivek Gautam , Rajendra Nayak , Vinayak Holikatti , "James E.J. Bottomley" , "Martin K. Petersen" , linux-scsi@vger.kernel.org, linux-arm-msm , Venkat Gopalakrishnan , Mark Rutland , Mathieu Malaterre , devicetree@vger.kernel.org, "linux-kernel@vger.kernel.org" List-Id: devicetree@vger.kernel.org On 7/23/2018 8:06 PM, Rob Herring wrote: > On Sun, Jul 22, 2018 at 9:20 PM Asutosh Das (asd) > wrote: >> >> 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 >>>> >>>> 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 >>>> Signed-off-by: Venkat Gopalakrishnan >>>> Signed-off-by: Can Guo >>>> Signed-off-by: Asutosh Das >>>> --- >>>> .../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? > > Right, not if it is a user decision. > >> When you say user-controlled, do you mean control it through sysfs entries? > > Yes. > >>> 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? > > The case that makes sense for this to be in DT is if there are h/w > limitations that prevent some low power modes. In such a case, that > limit is not likely specific to runtime PM or system suspend. > >>>> -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. > > The use-case can change in a running system. For example if you are > plugged in, then you probably don't want to enter a lower power mode. > > Rob > Ok - Thanks. I'm gonna make the following changes in v2: 1. Remove these entries from DT 2. Add support for these entries in sysfs. 3. Keep 3 as the default value for [rpm/spm]-levels -asd -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project