--- linux/Documentation/Configure.help-dist Tue Dec 18 14:30:02 2001 +++ linux/Documentation/Configure.help Tue Dec 18 18:44:11 2001 @@ -12541,6 +12541,30 @@ If you have an MGE Ellipse UPS, or you see timeouts in HID transactions, say Y; otherwise say N. +EHCI (USB 2.0) support +CONFIG_EHCI_HCD + The Enhanced Host Controller Interface (EHCI) is standard for USB 2.0 + "high speed" (480 Mbit/sec, 60 Mbyte/sec) host controller hardware. + If your USB host controller supports USB 2.0, you will likely want to + configure this Host Controller Driver. At this writing, the primary + implementation of EHCI is a chip from NEC, widely available in add-on + PCI cards, but implementations are in the works from other vendors + including Intel and Philips. Motherboard support is appearing. + + EHCI controllers are packaged with "companion" host controllers (OHCI + or UHCI) to handle USB 1.1 devices connected to root hub ports. Ports + will connect to EHCI if it the device is high speed, otherwise they + connect to a companion controller. If you configure EHCI, you should + probably configure the OHCI (for NEC and some other vendors) USB Host + Controller Driver too. + + You may want to read . + + This code is also available as a module ( = code which can be + inserted in and removed from the running kernel whenever you want). + The module will be called ehci-hcd.o. If you want to compile it as a + module, say M here and read . + UHCI (Intel PIIX4, VIA, ...) support CONFIG_USB_UHCI The Universal Host Controller Interface is a standard by Intel for --- /dev/null Thu Aug 24 02:00:32 2000 +++ linux/Documentation/usb/ehci.txt Tue Dec 18 16:43:07 2001 @@ -0,0 +1,164 @@ +18-Dec-2001 + +The EHCI driver is used to talk to high speed USB 2.0 devices using +USB 2.0-capable host controller hardware. The USB 2.0 standard is +compatible with the USB 1.1 standard. It defines three transfer speeds: + + - "High Speed" 480 Mbit/sec (60 MByte/sec) + - "Full Speed" 12 Mbit/sec (1.5 MByte/sec) + - "Low Speed" 1.5 Mbit/sec + +USB 1.1 only addressed full speed and low speed. High speed devices +can be used on USB 1.1 systems, but they slow down to USB 1.1 speeds. + +USB 1.1 devices may also be used on USB 2.0 systems. When plugged +into an EHCI controller, they are given to a USB 1.1 "companion" +controller, which is a OHCI or UHCI controller as normally used with +such devices. When USB 1.1 devices plug into USB 2.0 hubs, they +interact with the EHCI controller through a "Transaction Translator" +(TT) in the hub, which turns low or full speed transactions into +high speed "split transactions" that don't waste transfer bandwidth. + +At this writing, high speed devices are finally beginning to appear. +While usb-storage devices have been available for some time (working +quite speedily on the 2.4 version of this driver), hubs have only +very recently become available. + +Note that USB 2.0 support involves more than just EHCI. It requires +other changes to the Linux-USB core APIs, including the hub driver, +but those changes haven't needed to really change the basic "usbcore" +APIs exposed to USB device drivers. + +- David Brownell + + + +FUNCTIONALITY + +This driver is regularly tested on x86 hardware, and has also been +used on PPC hardware so big/little endianneess issues should be gone. +It's believed to do all the right PCI magic so that I/O works even on +systems with interesting DMA mapping issues. + +At this writing the driver should comfortably handle all control and bulk +transfers, including requests to USB 1.1 devices through transaction +translators (TTs) in USB 2.0 hubs. However, there some situations where +the hub driver needs to clear TT error state, which it doesn't yet do. + +Interrupt transfer support is newly functional and not yet as robust as +control and bulk traffic. As yet there is no support for split transaction +scheduling for interrupt transfers, which means among other things that +connecting USB 1.1 hubs, keyboards, and mice to USB 2.0 hubs won't work. +Connect them to USB 1.1 hubs, or to a root hub. + +Isochronous (ISO) transfer support is not yet working. No production +high speed devices are available which would need it (though high quality +webcams are in the works!). Note that split transaction support for ISO +transfers can't share much code with the code for high speed ISO transfers, +since EHCI represents these with a different data structure. + +The EHCI root hub code should hand off USB 1.1 devices to its companion +controller. This driver doesn't need to know anything about those +drivers; a OHCI or UHCI driver that works already doesn't need to change +just because the EHCI driver is also present. + +There are some issues with power management; suspend/resume doesn't +behave quite right at the moment. + + +USE BY + +Assuming you have an EHCI controller (on a PCI card or motherboard) +and have compiled this driver as a module, load this like: + + # modprobe ehci-hcd + +and remove it by: + + # rmmod ehci-hcd + +You should also have a driver for a "companion controller", such as +"ohci-hcd", "usb-ohci", "usb-uhci", or "uhci". In case of any trouble +with the EHCI driver, remove its module and then the driver for that +companion controller will take over (at lower speed) all the devices +that were previously handled by the EHCI driver. + +Module parameters (pass to "modprobe") include: + + log2_irq_thresh (default 0): + Log2 of default interrupt delay, in microframes. The default + value is 0, indicating 1 microframe (125 usec). Maximum value + is 6, indicating 2^6 = 64 microframes. This controls how often + the EHCI controller can issue interrupts. + +The EHCI interrupt handler just acknowledges interrupts and schedules +a tasklet to handle whatever needs handling. That keeps latencies low, +no matter how often interrupts are issued. + +Device drivers shouldn't care whether they're running over EHCI or not, +but they may want to check for "usb_device->speed == USB_SPEED_HIGH". +High speed devices can do things that full speed (or low speed) ones +can't, such as "high bandwidth" periodic (interrupt or ISO) transfers. + + +PERFORMANCE + +USB 2.0 throughput is gated by two main factors: how fast the host +controller can process requests, and how fast devices can respond to +them. The 480 Mbit/sec "raw transfer rate" is obeyed by all devices, +but aggregate throughput is also affected by issues like delays between +individual high speed packets, driver intelligence, and of course the +overall system load. Latency is also a performance concern. + +Bulk transfers are most often used where throughput is an issue. It's +good to keep in mind that bulk transfers are always in 512 byte packets, +and at most 13 of those fit into one USB 2.0 microframe. Eight USB 2.0 +microframes fit in a USB 1.1 frame; a microframe is 1 msec/8 = 125 usec. + +Hardware Performance + +At this writing, individual USB 2.0 devices tend to max out at around +20 MByte/sec transfer rates. This is of course subject to change; +and some devices now go faster, while others go slower. + +The NEC implementation of EHCI seems to have a hardware bottleneck +at around 28 MByte/sec aggregate transfer rate. While this is clearly +enough for a single device at 20 MByte/sec, putting three such devices +onto one bus does not get you 60 MByte/sec. The issue appears to be +that the controller hardware won't do concurrent USB and PCI access, +so that it's only trying six (or maybe seven) USB transactions each +microframe rather than thirteen. (Seems like a reasonable trade off +for a product that beat all the others to market by over a year!) +It's expected that newer implementations will better this, throwing +more silicon real estate at the problem so that new motherboard chip +sets will get closer to that 60 MByte/sec target. + +There's a minimum latency of one microframe (125 usec) for the host +to receive interrupts from the EHCI controller indicating completion +of requests. That latency is tunable; there's a module option. By +default ehci-hcd driver uses the minimum latency, which means that if +you issue a control or bulk request you can often expect to learn that +it completed in less than 250 usec (depending on transfer size). + +Software Performance + +To get even 20 MByte/sec transfer rates, Linux-USB device drivers will +need to keep the EHCI queue full. That means issuing large requests, +or using bulk queuing if a series of small requests needs to be issued. +When drivers don't do that, their performance results will show it. + +In typical situations, a usb_bulk_msg() loop writing out 4 KB chunks is +going to waste more than half the USB 2.0 bandwidth. Delays between the +I/O completion and the driver issuing the next request will take longer +than the I/O. If that same loop used 16 KB chunks, it'd be better; a +sequence of 128 KB chunks would waste a lot less. + +But rather than depending on such large I/O buffers to make synchronous +I/O be efficient, it's better to just queue all several (bulk) requests +to the HC, and wait for them all to complete (or be canceled on error). +Such URB queuing should work with all the USB 1.1 HC drivers too. + +TBD: Interrupt and ISO transfer performance issues. Those periodic +transfers are fully scheduled, so the main issue is likely to be how +to trigger "high bandwidth" modes. + --- linux/drivers/usb-dist/Config.in Tue Dec 18 14:30:30 2001 +++ linux/drivers/usb/Config.in Tue Dec 18 23:13:57 2001 @@ -18,7 +18,8 @@ bool ' Long timeout for slow-responding devices (some MGE Ellipse UPSes)' CONFIG_USB_LONG_TIMEOUT fi -comment 'USB Controllers' +comment 'USB Host Controller Drivers' +source drivers/usb/hcd/Config.in if [ "$CONFIG_USB_UHCI_ALT" != "y" ]; then dep_tristate ' UHCI (Intel PIIX4, VIA, ...) support' CONFIG_USB_UHCI $CONFIG_USB fi --- linux/drivers/usb-dist/Makefile Tue Dec 18 14:30:30 2001 +++ linux/drivers/usb/Makefile Tue Dec 18 18:32:45 2001 @@ -10,12 +10,12 @@ # Objects that export symbols. -export-objs := usb.o +export-objs := usb.o hcd.o # Multipart objects. list-multi := usbcore.o hid.o -usbcore-objs := usb.o usb-debug.o hub.o +usbcore-objs := usb.o usb-debug.o hub.o hcd.o hid-objs := hid-core.o hid-input.o ifneq ($(CONFIG_USB_PWC),n) @@ -80,6 +80,7 @@ # Object files in subdirectories +subdir-$(CONFIG_EHCI_HCD) += hcd subdir-$(CONFIG_USB_SERIAL) += serial subdir-$(CONFIG_USB_STORAGE) += storage