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5ce78af4 BP |
1 | /* |
2 | * IDE ATAPI streaming tape driver. | |
3 | * | |
4 | * This driver is a part of the Linux ide driver. | |
5 | * | |
6 | * The driver, in co-operation with ide.c, basically traverses the | |
7 | * request-list for the block device interface. The character device | |
8 | * interface, on the other hand, creates new requests, adds them | |
9 | * to the request-list of the block device, and waits for their completion. | |
10 | * | |
5ce78af4 BP |
11 | * The block device major and minor numbers are determined from the |
12 | * tape's relative position in the ide interfaces, as explained in ide.c. | |
13 | * | |
14 | * The character device interface consists of the following devices: | |
15 | * | |
16 | * ht0 major 37, minor 0 first IDE tape, rewind on close. | |
17 | * ht1 major 37, minor 1 second IDE tape, rewind on close. | |
18 | * ... | |
19 | * nht0 major 37, minor 128 first IDE tape, no rewind on close. | |
20 | * nht1 major 37, minor 129 second IDE tape, no rewind on close. | |
21 | * ... | |
22 | * | |
23 | * The general magnetic tape commands compatible interface, as defined by | |
24 | * include/linux/mtio.h, is accessible through the character device. | |
25 | * | |
26 | * General ide driver configuration options, such as the interrupt-unmask | |
27 | * flag, can be configured by issuing an ioctl to the block device interface, | |
28 | * as any other ide device. | |
29 | * | |
30 | * Our own ide-tape ioctl's can be issued to either the block device or | |
31 | * the character device interface. | |
32 | * | |
33 | * Maximal throughput with minimal bus load will usually be achieved in the | |
34 | * following scenario: | |
35 | * | |
36 | * 1. ide-tape is operating in the pipelined operation mode. | |
37 | * 2. No buffering is performed by the user backup program. | |
38 | * | |
39 | * Testing was done with a 2 GB CONNER CTMA 4000 IDE ATAPI Streaming Tape Drive. | |
40 | * | |
41 | * Here are some words from the first releases of hd.c, which are quoted | |
42 | * in ide.c and apply here as well: | |
43 | * | |
44 | * | Special care is recommended. Have Fun! | |
45 | * | |
5ce78af4 BP |
46 | * Possible improvements. |
47 | * | |
48 | * 1. Support for the ATAPI overlap protocol. | |
49 | * | |
50 | * In order to maximize bus throughput, we currently use the DSC | |
51 | * overlap method which enables ide.c to service requests from the | |
52 | * other device while the tape is busy executing a command. The | |
53 | * DSC overlap method involves polling the tape's status register | |
54 | * for the DSC bit, and servicing the other device while the tape | |
55 | * isn't ready. | |
56 | * | |
57 | * In the current QIC development standard (December 1995), | |
58 | * it is recommended that new tape drives will *in addition* | |
59 | * implement the ATAPI overlap protocol, which is used for the | |
60 | * same purpose - efficient use of the IDE bus, but is interrupt | |
61 | * driven and thus has much less CPU overhead. | |
62 | * | |
63 | * ATAPI overlap is likely to be supported in most new ATAPI | |
64 | * devices, including new ATAPI cdroms, and thus provides us | |
65 | * a method by which we can achieve higher throughput when | |
66 | * sharing a (fast) ATA-2 disk with any (slow) new ATAPI device. | |
67 | */ |