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diff --git a/Documentation/usb/uhci.txt b/Documentation/usb/uhci.txt deleted file mode 100644 index 2f25952c86c6..000000000000 --- a/Documentation/usb/uhci.txt +++ /dev/null @@ -1,165 +0,0 @@ -Specification and Internals for the New UHCI Driver (Whitepaper...) - - brought to you by - - Georg Acher, acher@in.tum.de (executive slave) (base guitar) - Deti Fliegl, deti@fliegl.de (executive slave) (lead voice) - Thomas Sailer, sailer@ife.ee.ethz.ch (chief consultant) (cheer leader) - - $Id: README.uhci,v 1.1 1999/12/14 14:03:02 fliegl Exp $ - -This document and the new uhci sources can be found on - http://hotswap.in.tum.de/usb - -1. General issues - -1.1 Why a new UHCI driver, we already have one?!? - -Correct, but its internal structure got more and more mixed up by the (still -ongoing) efforts to get isochronous transfers (ISO) to work. -Since there is an increasing need for reliable ISO-transfers (especially -for USB-audio needed by TS and for a DAB-USB-Receiver build by GA and DF), -this state was a bit unsatisfying in our opinion, so we've decided (based -on knowledge and experiences with the old UHCI driver) to start -from scratch with a new approach, much simpler but at the same time more -powerful. -It is inspired by the way Win98/Win2000 handles USB requests via URBs, -but it's definitely 100% free of MS-code and doesn't crash while -unplugging an used ISO-device like Win98 ;-) -Some code for HW setup and root hub management was taken from the -original UHCI driver, but heavily modified to fit into the new code. -The invention of the basic concept, and major coding were completed in two -days (and nights) on the 16th and 17th of October 1999, now known as the -great USB-October-Revolution started by GA, DF, and TS ;-) - -Since the concept is in no way UHCI dependent, we hope that it will also be -transferred to the OHCI-driver, so both drivers share a common API. - -1.2. Advantages and disadvantages - -+ All USB transfer types work now! -+ Asynchronous operation -+ Simple, but powerful interface (only two calls for start and cancel) -+ Easy migration to the new API, simplified by a compatibility API -+ Simple usage of ISO transfers -+ Automatic linking of requests -+ ISO transfers allow variable length for each frame and striping -+ No CPU dependent and non-portable atomic memory access, no asm()-inlines -+ Tested on x86 and Alpha - -- Rewriting for ISO transfers needed - -1.3. Is there some compatibility to the old API? - -Yes, but only for control, bulk and interrupt transfers. We've implemented -some wrapper calls for these transfer types. The usbcore works fine with -these wrappers. For ISO there's no compatibility, because the old ISO-API -and its semantics were unnecessary complicated in our opinion. - -1.4. What's really working? - -As said above, CTRL and BULK already work fine even with the wrappers, -so legacy code wouldn't notice the change. -Regarding to Thomas, ISO transfers now run stable with USB audio. -INT transfers (e.g. mouse driver) work fine, too. - -1.5. Are there any bugs? - -No ;-) -Hm... -Well, of course this implementation needs extensive testing on all available -hardware, but we believe that any fixes shouldn't harm the overall concept. - -1.6. What should be done next? - -A large part of the request handling seems to be identical for UHCI and -OHCI, so it would be a good idea to extract the common parts and have only -the HW specific stuff in uhci.c. Furthermore, all other USB device drivers -should need URBification, if they use isochronous or interrupt transfers. -One thing missing in the current implementation (and the old UHCI driver) -is fair queueing for BULK transfers. Since this would need (in principle) -the alteration of already constructed TD chains (to switch from depth to -breadth execution), another way has to be found. Maybe some simple -heuristics work with the same effect. - ---------------------------------------------------------------------------- - -2. Internal structure and mechanisms - -To get quickly familiar with the internal structures, here's a short -description how the new UHCI driver works. However, the ultimate source of -truth is only uhci.c! - -2.1. Descriptor structure (QHs and TDs) - -During initialization, the following skeleton is allocated in init_skel: - - framespecific | common chain - -framelist[] -[ 0 ]-----> TD --> TD -------\ -[ 1 ]-----> TD --> TD --------> TD ----> QH -------> QH -------> QH ---> NULL - ... TD --> TD -------/ -[1023]-----> TD --> TD ------/ - - ^^ ^^ ^^ ^^ ^^ ^^ - 1024 TDs for 7 TDs for 1 TD for Start of Start of End Chain - ISO INT (2-128ms) 1ms-INT CTRL Chain BULK Chain - -For each CTRL or BULK transfer a new QH is allocated and the containing data -transfers are appended as (vertical) TDs. After building the whole QH with its -dangling TDs, the QH is inserted before the BULK Chain QH (for CTRL) or -before the End Chain QH (for BULK). Since only the QH->next pointers are -affected, no atomic memory operation is required. The three QHs in the -common chain are never equipped with TDs! - -For ISO or INT, the TD for each frame is simply inserted into the appropriate -ISO/INT-TD-chain for the desired frame. The 7 skeleton INT-TDs are scattered -among the 1024 frames similar to the old UHCI driver. - -For CTRL/BULK/ISO, the last TD in the transfer has the IOC-bit set. For INT, -every TD (there is only one...) has the IOC-bit set. - -Besides the data for the UHCI controller (2 or 4 32bit words), the descriptors -are double-linked through the .vertical and .horizontal elements in the -SW data of the descriptor (using the double-linked list structures and -operations), but SW-linking occurs only in closed domains, i.e. for each of -the 1024 ISO-chains and the 8 INT-chains there is a closed cycle. This -simplifies all insertions and unlinking operations and avoids costly -bus_to_virt()-calls. - -2.2. URB structure and linking to QH/TDs - -During assembly of the QH and TDs of the requested action, these descriptors -are stored in urb->urb_list, so the allocated QH/TD descriptors are bound to -this URB. -If the assembly was successful and the descriptors were added to the HW chain, -the corresponding URB is inserted into a global URB list for this controller. -This list stores all pending URBs. - -2.3. Interrupt processing - -Since UHCI provides no means to directly detect completed transactions, the -following is done in each UHCI interrupt (uhci_interrupt()): - -For each URB in the pending queue (process_urb()), the ACTIVE-flag of the -associated TDs are processed (depending on the transfer type -process_{transfer|interrupt|iso}()). If the TDs are not active anymore, -they indicate the completion of the transaction and the status is calculated. -Inactive QH/TDs are removed from the HW chain (since the host controller -already removed the TDs from the QH, no atomic access is needed) and -eventually the URB is marked as completed (OK or errors) and removed from the -pending queue. Then the next linked URB is submitted. After (or immediately -before) that, the completion handler is called. - -2.4. Unlinking URBs - -First, all QH/TDs stored in the URB are unlinked from the HW chain. -To ensure that the host controller really left a vertical TD chain, we -wait for one frame. After that, the TDs are physically destroyed. - -2.5. URB linking and the consequences - -Since URBs can be linked and the corresponding submit_urb is called in -the UHCI-interrupt, all work associated with URB/QH/TD assembly has to be -interrupt save. This forces kmalloc to use GFP_ATOMIC in the interrupt. |
