Abstract:
A method and system for allowing a processor to enter low power states in an information handling system (IHS) includes detecting an access request for a bus mastering device. The method and system also includes in response to failing to detect an access request for the bus mastering device within a period of time, suspending a bus mastering device controller associated with the bus mastering device, wherein the now suspended bus mastering controller no longer prevents the processor from entering low power states.

Description:
BACKGROUND  
       [0001]     The present disclosure relates generally to information handling systems (IHS&#39;s), and more particularly to information handling systems which feature reduced power consumption.  
         [0002]     As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.  
         [0003]     As power conservation is an ever present issue, many modern IHS&#39;s are designed with power savings features. A common method used in IHS&#39;s to achieve lower power usage is to configure IHS&#39;s and components with multiple power states. For example, according to the current Advanced Configuration and Power Interface (ACPI) standard, a typical IHS may enter into power savings states ranging from S0 (full on) to S4 (hibernate). More relevant to this disclosure, Intel Architecture based processors may operate in various power savings states known as “C states”, ranging from C0 (full power—least power saving state) to C4 (highest power saving state). Because “C States” higher than C2 present significantly greater power savings, it would be desirable for processors to operate in C3 and higher states whenever possible.  
         [0004]     IHS&#39;s which feature bus mastering components present significant hurdles to achieving C3 and higher power savings states because any bus mastering activity prevents processors from entering C3 and higher states. One example of a type of component which utilizes bus mastering is Universal Serial Bus (USB). USB component&#39;s prevalence in modern IHS&#39;s presents an acute challenge in designing more power efficient IHS&#39;s.  
         [0005]     Some existing USB devices support power savings states through what is known as “selective-suspend.” “Selective-suspend” allows USB hubs to be suspended if no devices are connected to the hub. In addition, if only suspended USB devices are connected to a USB controller, the controller may also be suspended. Therefore, IHS&#39;s equipped with only “selective-suspend” compliant USB devices may operate with their processors in C3 and higher states. However, many USB devices do not support “selective-suspend.” This is especially true for USB storage devices.  
         [0006]     Therefore, what is needed is a technique for enabling an IHS equipped with a bus mastering device, such as a non selective-suspend compliant USB device, to operate with its processor in enhanced power savings states such as C3 and higher states to reduce power consumption.  
       SUMMARY  
       [0007]     Accordingly, in one embodiment, a method for allowing a processor to enter low power states in an IHS is disclosed which includes detecting an access request for a bus mastering device. The method also includes in response to failing to detect an access request for the bus mastering device within a predetermined period of time, suspending a bus mastering device controller associated with the bus mastering device, wherein the now suspended bus mastering controller no longer prevents the processor from entering low power states.  
         [0008]     In another embodiment, an information handling system (IHS) is disclosed which includes a processor capable of entering low power states. The IHS includes a memory coupled to the processor and a non-volatile storage coupled to the processor. The IHS also includes a bus mastering device and a bus mastering device controller coupled to the bus mastering device and the processor for transferring information between the bus mastering device and the processor. Executable code is stored in the non-volatile storage for detecting an access request for the bus mastering device and causing the bus mastering device controller to be suspended in response to failing to detect an access request for the bus mastering device within a predetermined period of time, wherein the now suspended controller no longer prevents the processor from entering low power states.  
         [0009]     A principal advantage of the embodiment disclosed herein is that the IHS can operate with its processor in low power states, resulting in reduction in power consumption. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a block diagram of the disclosed information handling system.  
         [0011]      FIG. 2A  is a flow chart showing the filter driver initialization process in the information handling system of  FIG. 1 .  
         [0012]      FIG. 2B  is a flow chart showing the process flow of suspending the USB controller in the information handling system of  FIG. 1 .  
         [0013]      FIG. 2C  is a flow chart showing the process flow of resuming operation of the USB controller in the information handling system of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION  
       [0014]     For purposes of this disclosure, an information handling system may include any instrumentality or aggregate of instrumentalities operable to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, or other purposes. For example, an information handling system may be a personal computer, a network storage device, or any other suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include random access memory (RAM), one or more processing resources such as a central processing unit (CPU) or hardware or software control logic, ROM, and/or other types of nonvolatile memory. Additional components of the information handling system may include one or more disk drives, one or more network ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, and a video display. The information handling system may also include one or more buses operable to transmit communications between the various hardware components.  
         [0015]     In one embodiment, information handling system  100 ,  FIG. 1 , includes a processor  105  such as an Intel Pentium series processor. Processor  105  is capable of operating in one of the above mentioned “C states” to conserve power. An Intel Hub Architecture (IHA) chipset  110  provides IHS system  100  with graphics/memory controller hub functions and I/O functions. More specifically, IHA chipset  110  acts as a host controller which communicates with a graphics controller  115  coupled thereto. A display  120  is coupled to graphics controller  115 . Chipset  110  further acts as a controller for main memory  130  which is coupled thereto. Chipset  110  also acts as an I/O controller hub (ICH) which performs I/O functions. A super input/output (I/O) controller  140  is coupled to chipset  110  to provide communications between chipset  110  and input devices  145  such as a mouse, keyboard, and tablet, for example. A USB controller  152  is coupled to chipset  110  so that devices such as a USB device  154  can be connected to chipset  110  and processor  105 . USB device  154  is coupled to USB controller  152  via USB  150 . USB devices that may be coupled to USB controller  152  include floppy disk drives, CD-ROM drives, DVD-ROM drives and other devices which support the USB standard. System basic input-output system (BIOS)  160  is coupled to chipset  110  as shown. BIOS  160  is stored in CMOS or FLASH memory so that it is nonvolatile.  
         [0016]     A local area network (LAN) controller  170 , alternatively called a network interface controller (NIC), is coupled to chipset  110  to facilitate connection of system  100  to other information handling systems. Media driver controller  180  is coupled to chipset  110  so that devices such as media drives  185  can be connected to chipset  110  and processor  105 . Devices that can be coupled to media controller  180  include CD-ROM drives, DVD drives, hard disk drives and other fixed or removable media drives. An expansion bus  190 , such as a peripheral component interconnect (PCI) bus, PCI Express bus, serial advanced technology attachment (SATA) bus or other bus is coupled to chipset  110  as shown. Expansion bus  190  includes one or more expansion slots (not shown) for receiving expansion cards which provide IHS  100  with additional functionality.  
         [0017]     USB  150 , USB controller  152 , and USB device  154  feature bus mastering. USB device  154  is an example of a bus mastering device and USB controller  152  is an example of a bus mastering device controller. As discussed earlier, in conventional systems, any bus mastering activity prevents processor  105  from being placed into states C3 and higher. Also as mentioned above, although “selective suspend” allows some USB equipped IHS&#39;s to place their processors in C3 and higher states, all USB devices in an IHS must support “selective suspend” in order for this feature to operate. Here, USB device  154  is not a “selective suspend” compliant device. To remedy the power issue related to devices featuring bus mastering, and particularly in this embodiment with USB devices, IHS  100  includes additional features as described herein.  
         [0018]     While IHS  100  is actively operational, an application  136  is loaded in main memory  130 . Application  136  may be a word processing application, graphics editor, or any other available software application. Also loaded in main memory  130  is an operating system (OS)  132 , such as one of Microsoft Windows family of operating systems. (Microsoft and Windows are trademarks of Microsoft Corp.). In this embodiment, OS  132  includes a USB stack  133  and a filter driver  134  which is stored in the form of executable code. Main memory further includes a USB state flag  138 . Although USB state flag  138  is shown to be loaded in main memory  130  here, in other embodiments, USB state flag may be stored in other types of volatile and non-volatile storage devices such as media drives  185  or BIOS  160 .  
         [0019]     Operation of IHS  100  may be seen by examining  FIGS. 2A, 2B , and  2 C.  FIG. 2A  is a flow chart depicting process flow that occurs when filter driver  134  initializes. In block  200 , filter driver  134  is loaded into main memory  130 . Subsequently in block  205 , filter driver  134  starts a timer (not shown) for a period of time. The period of time represents an amount of time that USB controller  152  may remain inactive before a process to suspend USB controller  152  initiates. For example, the timer may be set for 10 seconds, and if USB controller  152  remains inactive for 10 seconds, a process will begin to suspend USB controller  152 . In block  210 , filter driver  134  clears USB state flag  138 . USB state flag  138  may either be cleared which is its default state, or in the alternative, set. Functions of USB state flag  138  as well as the timer are discussed in more detail later in this disclosure.  
         [0020]      FIG. 2B  is a flow chart illustrating the steps IHS  100  takes to suspend USB controller  152  in the event the aforementioned timer expires. As discussed above, the timer expires if USB controller  152  remains inactive for the period of time for which the timer is set. IHS  100  may be configured to detect USB controller  152 &#39;s inactivity in a number of different ways. In this particular embodiment, the executable code of filter driver  134  is configured to monitor input/output request packets (IRP&#39;s) generated for USB controller  152 . IRP&#39;s are generated by OS  132  in response to requests made by OS  132  itself or by application  136 , to transmit or receive information to or from devices coupled to USB controller  152 , such as USB device  154 . Using a word processing application and a floppy disk drive as examples of application  136  and USB device  154 , respectively, when an IHS user issues a command to save a document to a disk inserted into the floppy disk drive, the word processing application causes OS  132  to generate an IRP in performing the task. IRP&#39;s are then transmitted to USB stack  133  for further processing. While in transmission, IRP&#39;s are detected by filter driver  134 . As discussed in more detail later, detection of IRP&#39;s by filter driver  134  indicates that USB controller  152  is currently active, and the timer is restarted. Of course, restarting the timer prevents it from expiring.  
         [0021]     If filter driver  134  fails to detect an IRP during the period of time as set by the timer, the timer expires. In the event that the timer expires as shown in block  220 , filter driver  134  determines whether USB controller  152  is currently on (i.e., not suspended) as shown in decision block  225 . If filter driver  134  determines that USB controller  152  is currently not in suspend mode, filter driver  134  causes USB controller  152  to be placed into suspend mode as shown in block  230 . Various implementations are possible to cause USB controller  152  to be placed into suspend mode. In one particular embodiment, filter driver  134  may cause a system management interrupt (SMI) to be generated, which in turn places USB controller  152  into suspend mode. In addition, filter driver  134  may similarly place USB device  154  into suspend mode prior to placing controller  152  into suspend mode.  
         [0022]     As shown in block  235 , filter driver  134  also sets USB state flag  138 . As mentioned earlier, USB state flag  138  may be set or in the alternative, cleared. When USB flag  138  is set, it functions as an indication that USB controller  152  is suspended and that when filter driver  134  needs to resume operation of controller  152  (for example, because it now detects an IRP destined for USB controller  152 ), it is permitted to do so. Essentially, setting USB flag  138  is an indication that filter driver  134  and not another component of IHS  100  caused USB controller  152  to be placed into suspend mode. In the present disclosure, USB controller  152  is placed into suspend mode by filter driver  134 . However, in the course of IHS  100 &#39;s operation, controller  152  may be placed into suspend mode by various other components of IHS  100 , such as other components of OS  132 . It is desirable to prevent filter driver  134  from resuming operation of USB controller  152  that has been placed into suspend mode by another component of IHS  100 . Accordingly, when the time arrives for resuming operation of USB controller  152 , USB state flag  138  aids filter driver  138  in distinguishing between situations where it may perform the operation (when it is set), and situations where it must defer (when it is cleared) to the component which originally placed controller  152  into suspend mode. The process of resuming operation of controller  152  is discussed in more detail later in this disclosure.  
         [0023]     At the completion of above procedures, USB controller  152 , now suspended, no longer prevents processor  105  from entering into C3 and higher states, as shown in block  240 . Placing USB controller  152  into suspend mode stops bus mastering activities normally engaged by controller  152 . Note that if the test conducted at decision block  225  determines that USB controller  152  is already in suspend mode, then the above steps are skipped as shown in  FIG. 2B  and the flow directly continues to block  240 .  
         [0024]      FIG. 2C  is a flow chart describing the process flow of resuming operation of USB controller  152 . The process is initiated when OS  132  generates an IRP for USB controller  152  during the period of time in which the timer has not expired. As shown in block  250 , the IRP is detected, and in this particular embodiment, filter driver  134  performs the detection. Detection of the IRP by filter driver  134  indicates a new activity, and filter driver  134  restarts the timer for the period time as illustrated in block  255  to begin measuring time of inactivity anew.  
         [0025]     In decision block  260 , a test is conducted to determine whether USB state flag  138  is set. As noted earlier, when USB state flag is set, it is an indication that USB controller  152  is currently in suspend mode. It is also an indication that filter driver  134  and not another component of IHS  100  caused USB controller  152  to be placed into suspend mode. Consequently, if it is determined that USB state flag  138  is in fact set, filter driver  134  takes the necessary steps to resume operation of USB controller  152  as shown in block  270 . In one embodiment, resuming operation of controller  152  is performed by filter driver  134  by generating a SMI, which in turn actually resumes operation of controller  152 . Additionally, resuming operation of controller  152  may include resuming operation of USB device  154  coupled to controller  152 . If an alternative outcome is reached in decision block  260  and USB state flag  138  is not set, then it is an indication that controller  152  was placed into suspend mode by another component of IHS  100  or that it was not placed into suspend mode at all. Accordingly, the flow continues directly to block  275  where IHS  100  proceeds with normal input/output (I/O) operation as shown, relying on another component as necessary to resume operation of USB controller  152  if controller  152  was placed in suspend mode by the other component.  
         [0026]     Once filter driver  134  resumes operation of USB controller  152  in block  265 , filter driver  134  clears USB state flag  138  as shown in block  270  to indicate that controller  152  is currently not in suspend mode. Finally, IHS  100  proceeds with normal I/O operation as shown in block  275 .  
         [0027]     Note that in the above discussion, a number of functions related to detecting IRP&#39;s, placing USB controller  152  into suspend mode, resuming operation of controller  152 , and other aspects of present disclosure are incorporated into filter driver  134 . However, in another embodiment, functions described therein may be performed by any one or more software components and/or hardware components so configured.  
         [0028]     Although illustrative embodiments have been shown and described, a wide range of modification, change and substitution is contemplated in the foregoing disclosure and in some instances, some features of the embodiments may be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the embodiments disclosed herein.