Introduction to UFS CLK gate

One . UFS Clk Gate  summary

1.  What is? UFS Clk Gate

UFS Clk Gate yes UFS Host Controller Driver A function of ,  refer to UFS System  In my spare time , take UFS Clock close , And let UFS MPHY Link Get into Hibernate state , Reduce the overhead of system resources .

2.  What is? UFS Clock

Host Memory(DDR Memory ) and UFS Host Controller Data communication is through AIX Bus transmission , among UFS Clock refer to AXI Clock on bus , at present Soc It's usually used 300MHz Of UFS Clock.

 

3.  UFS Clk Gate Support for

at present Qcom The platform and MTK Platform support UFS Clk Gate function ,Hisilicon970 Platform does not support Clk Gate.

according to ARM And the energy-saving strategy of the kernel , I hope more and more platforms support Clk Gate function , This can also prove ARM And the low power consumption of the kernel .

Two . UFS Clk Gate Detail 

1.  UFS CLK Gate Init Initialization flow

(1). Set up related worker Used to close UFS CLK And on UFS CLK Function of .

(2). Set high accuracy Timer, Call at the right time ufs clk gate work and ufs clk ungate work The timing of .

gate_work: worker to turn off clocks

ungate_work: worker to turn on clocks that will be used in case of interrupt context

(3). Set the delay time in power saving mode and performance mode ,

(4). register CLK Gate relevant sysfs Interface

#define UFSHCD_CLK_GATING_DELAY_MS_PWR_SAVE 10 #define UFSHCD_CLK_GATING_DELAY_MS_PERF    50 

2 . UFS CLK Gate Work technological process

Gate Work technological process ：

(1). UFS When command processing is complete ,UFS Device Returns the Response UPIU to UFS Host, UFS Host Create an interrupt ,CPU Enter the interrupt processing function to process .

(2). What the interrupt handler mainly does ： Will check Doorbell Whether to clear ,Response UPIU Are there any mistakes , Check Doorbell It's cleared ,Reponse UPIU There are no mistakes , Then release relevant resources , close UFS CLK.

(3). The present state is ： Check Doorbell It's cleared ,Reponse UPIU There are no mistakes , You can call __ufshcd_release close UFS CLK.

(4). close CLK I'll check it before UFS Host Controllert Do you support CLK Gate, If not, exit directly , If you support it, keep going .

(5). Reduce clk gating active request Count . Note: Only when clk gating active request Count as 0 When , To shut down UFS CLK.

(6). Check Block CLK Gating Enter The location of ： active_reqs/lrb_in_use/outstanding_tasks/active_uic_cmd/uic_async_done

active_reqs: number of requests that are pending and should be waited for completion before gating clocks

lrb_in_use:  lrb in use

outstanding_tasks: Bits representing outstanding task requests

active_uic_cmd: handle of active UIC command

uic_async_done:  uic cmd complete flag

(7). (re)start an hrtimer, start-up hrtimer, Then interval clk gating delay_ms after , call gating->gate_hrtimer.function = ufshcd_clkgate_hrtimer_handler;

(8). handler What we mainly do is drive queue clk_gating.gate_work, Get into ufs clk gate work Interface processing .

(9).   take UFS adjoining course (Unipro/MPHY) Put it in Hibernate state , Then close it UFS CLK . 

3.UFS CLK UnGate Work technological process

Gate Work technological process ：

(1). When you need to access UFS When , Need assurance UFS Host Driver yes Resume The state of , adjoining course (UniPro/MPHY) yes Active The state of ,UFS Clock The state to be opened .

(2).ufshcd_hold The thing to do is Enable UFS Clock and exit from hibern8 mode and set the link as active.

(3) . Turn on CLK I'll check it before UFS Host Controllert Do you support CLK Gate, If not, exit directly , If you support it, keep going .

(4). increase clk gating active request Count . Note: Only when clk gating active request Count as 0 When , To shut down UFS CLK.

(5). Check clk_gating state： CLKS_ON/REQ_CLKS_OFF/CLKS_OFF/REQ_CLKS_ON CLKS_ON: If it is in this state , Would call UFS clk ungate work REQ_CLKS_OFF: If it is in this state , Will CLK Gate The status is set to REQ_CLKS_ON, And then call UFS clk ungate work CLKS_OFF: If it is in this state , Will try to cancel UFS CLK gate work REQ_CLKS_ON: If this state , Satisfy Link yes Hibernate Status and support Hibern8 during gating when , Would call UFS clk ungate work.

(6). UFS clk ungate work The thing to do is to open it first UFS CLK., And then UFS adjoining course (Unipro/MPHY) Hibernate State exit , Make the connection layer become Active state .

3、 ... and , Reference material

1. UFS Driver code

2. UFS agreement