On Tue, Dec 13, 2016 at 2:16 PM, Subhash Jadavani <subhashj@xxxxxxxxxxxxxx> wrote: > 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@xxxxxxxxxxxxxx> >>> Signed-off-by: Subhash Jadavani <subhashj@xxxxxxxxxxxxxx> >>> --- >>> .../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. What latencies can be tolerated is going to depend on the application and could vary while running, so putting in DT doesn't make sense. I would break down settings like this: broken h/w -> DT user tuning/config -> sysfs sensible defaults -> driver > 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. The driver can tie the states to together if needed. Just document what's broken in DT and let the driver make decisions. Rob -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
