From bab5271ec189c6a0da511029b833863e901b5e13 Mon Sep 17 00:00:00 2001 From: David Brownell Date: Thu, 25 Apr 2002 22:14:02 -0700 Subject: [PATCH] [PATCH] PATCH 2.5.10 ehci.txt USB ehci documentation update It mostly updates the description of the EHCI driver to point out that several non-NEC implementations are now expected to work, and that (high speed) ISO is supported. --- Documentation/usb/ehci.txt | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/Documentation/usb/ehci.txt b/Documentation/usb/ehci.txt index 205d412ae38e..9691ec956558 100644 --- a/Documentation/usb/ehci.txt +++ b/Documentation/usb/ehci.txt @@ -1,4 +1,4 @@ -18-Dec-2001 +26-Apr-2002 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 @@ -19,6 +19,9 @@ 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, this driver has been seen to work with implementations +of EHCI from (in alphabetical order): Intel, NEC, Philips, and VIA. + 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 @@ -36,7 +39,7 @@ APIs exposed to USB device drivers. 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. +used on PPC hardware so big/little endianness 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. @@ -51,11 +54,13 @@ 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 +Isochronous (ISO) transfer support is also newly functional. 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. +since EHCI represents these with a different data structure. So for now, +most USB audio and video devices have the same restrictions as hubs, mice, +and keyboards: don't connect them using high speed USB hubs. 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 @@ -99,6 +104,8 @@ 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. +Also, some values in device descriptors (such as polling intervals for +periodic transfers) use different encodings when operating at high speed. PERFORMANCE -- 2.39.5