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Annotation of coherent/b/STREAMS/i386/dmalock.c, revision 1.1

1.1     ! root        1: /* $Header: /src386/STREAMS/i386/RCS/dmalock.c,v 2.3 93/08/09 13:39:02 bin Exp Locker: bin $
        !             2:  *
        !             3:  *     The  information  contained herein  is a trade secret  of INETCO
        !             4:  *     Systems, Ltd, and is  confidential information.   It is provided
        !             5:  *     under a license agreement,  and may be copied or disclosed  only
        !             6:  *     under  the  terms  of  that  agreement.    Any  reproduction  or
        !             7:  *     disclosure  of  this   material   without  the  express  written
        !             8:  *     authorization of INETCO Systems, Ltd. or persuant to the license
        !             9:  *     agreement is unlawful.
        !            10:  *
        !            11:  *     Copyright (c) 1989
        !            12:  *     An unpublished work by INETCO Systems, Ltd.
        !            13:  *     All rights reserved.
        !            14:  *
        !            15:  * $Description: $
        !            16:  *     Routines to lock/unlock the DMA controller chip.
        !            17:  *
        !            18:  * $Author: bin $
        !            19:  *
        !            20:  * $Creation: June 21, 1989 $
        !            21:  *
        !            22:  * $Log:       dmalock.c,v $
        !            23:  * Revision 2.3  93/08/09  13:39:02  bin
        !            24:  * Kernel 82 changes
        !            25:  * 
        !            26:  * Revision 2.2  93/07/26  13:55:59  nigel
        !            27:  * Nigel's R80
        !            28:  * 
        !            29:  * Revision 1.1  93/04/14  10:26:34  root
        !            30:  * r75
        !            31:  * 
        !            32:  * Revision 1.1        89/06/30  16:21:26      src
        !            33:  * Initial revision
        !            34:  * 
        !            35:  */
        !            36: 
        !            37: #include <kernel/timeout.h>
        !            38: 
        !            39: typedef void (* vfp_t)();              /* Void function pointer type.       */
        !            40: 
        !            41: /*
        !            42:  * If the following variable is non-zero, DMA controller locking is enabled,
        !            43:  * allowing at access to only one DMA channel at a time.
        !            44:  */
        !            45: int DMALCK = 1;
        !            46: 
        !            47: static TIM * dmatail = (TIM *)0;       /* DMA deferred function queue tail. */
        !            48: static TIM * dmahead = (TIM *)0;       /* DMA deferred function queue head. */
        !            49: 
        !            50: /*
        !            51:  * int
        !            52:  * dmalock( dfp, fun, arg )
        !            53:  * TIM * dfp;
        !            54:  * vfp_t fun;
        !            55:  * int  arg;
        !            56:  *
        !            57:  *     Inputs: dfp  = Deferred function structure pointer.
        !            58:  *             fun  = Function to call if request is deferred.
        !            59:  *             arg  = Argument to pass to function.
        !            60:  *
        !            61:  *     Action: Either locks DMA controller immediately or defers function
        !            62:  *             call until lock can be granted.
        !            63:  *
        !            64:  *     Return: 0 = Lock granted or -1 = Lock deferred.
        !            65:  *
        !            66:  *     Notes:  DMA controller locking was introduced to cure a bug on the
        !            67:  *             NCR DMA controller, where overlapped DMA caused problems.
        !            68:  *             No action is taken if DMA locking is disabled.
        !            69:  */
        !            70: 
        !            71: int
        !            72: dmalock( dfp, fun, arg )
        !            73: register TIM  * dfp;
        !            74: vfp_t          fun;
        !            75: int            arg;
        !            76: {
        !            77:        register int s;         /* Interrupt mask state. */
        !            78: 
        !            79:        /*
        !            80:         * If DMA locking is disabled, allow functions to proceed.
        !            81:         */
        !            82:        if ( DMALCK == 0 )
        !            83:                return( 0 );
        !            84: 
        !            85:        /*
        !            86:         * Record function and argument to be invoked upon dmaunlock.
        !            87:         */
        !            88:        dfp->t_func = fun;
        !            89:        dfp->t_farg = arg;
        !            90:        dfp->t_next = (TIM *)0;
        !            91: 
        !            92:        s = sphi();
        !            93: 
        !            94:        /*
        !            95:         * If the queue is empty, put our structure at the head.
        !            96:         */
        !            97:        if ( dmahead == (TIM *)0 ) {
        !            98:                dmahead = dfp;
        !            99:                dmatail = dfp;
        !           100:                spl( s );
        !           101:                return( 0 );
        !           102:        }
        !           103: 
        !           104:        /*
        !           105:         * PARANOIA:    If our structure is already at the head of the queue,
        !           106:         *              print a message and return.
        !           107:         */
        !           108:        if ( dmahead == dfp ) {
        !           109:                spl( s );
        !           110:                printf( "dmalock: driver attempting to doubly lock DMA controller.\n" );
        !           111:                return( 0 );
        !           112:        }
        !           113: 
        !           114:        /*
        !           115:         * Append to tail of DMA deferred function queue.
        !           116:         */
        !           117:        dmatail->t_next = dfp;
        !           118:        dmatail         = dfp;
        !           119:        spl( s );
        !           120:        return( -1 );
        !           121: }
        !           122: 
        !           123: /*
        !           124:  * void
        !           125:  * dmaunlock( dfp )
        !           126:  * TIM * dfp;
        !           127:  *
        !           128:  *     Inputs: dfp = Deferred function structure pointer.
        !           129:  *
        !           130:  *     Action: Unlocks the DMA controller and calls the next deferred
        !           131:  *             function, if any.
        !           132:  *
        !           133:  *     Notes:  No action is taken if the deferred function structure pointer
        !           134:  *             is not the same as the one used to lock the DMA controller.
        !           135:  */
        !           136: 
        !           137: void
        !           138: dmaunlock( dfp )
        !           139: register TIM * dfp;
        !           140: {
        !           141:        register TIM *  qp;     /* Temporary function queue pointer.    */
        !           142:        register int    s;      /* Interrupt mask state.                */
        !           143: 
        !           144:        s = sphi();
        !           145: 
        !           146:        /*
        !           147:         * If the DMA controller is not locked, return.
        !           148:         */
        !           149:        if ( dmahead == (TIM *)0 ) {
        !           150:                spl( s );
        !           151:                return;
        !           152:        }
        !           153: 
        !           154:        /*
        !           155:         * If our lock is not the one holding the DMA controller:
        !           156:         */
        !           157:        if ( dmahead != dfp ) {
        !           158: 
        !           159:                /*
        !           160:                 * Look for us in queue.
        !           161:                 */
        !           162:                for ( qp = dmahead; qp != dmatail; qp = qp->t_next )
        !           163: 
        !           164:                        /*
        !           165:                         * If found, remove us.
        !           166:                         */
        !           167:                        if ( qp->t_next == dfp ) {
        !           168:                                qp->t_next = dfp->t_next;
        !           169: 
        !           170:                                if ( dmatail == dfp )
        !           171:                                        dmatail = qp;
        !           172: 
        !           173:                                break;
        !           174:                        }
        !           175: 
        !           176:                spl( s );
        !           177:                return;
        !           178:        }
        !           179: 
        !           180:        /*
        !           181:         * If there are no functions waiting for us, empty queue and return.
        !           182:         */
        !           183:        if ( dmahead == dmatail ) {
        !           184:                dmahead = (TIM *)0;
        !           185:                spl( s );
        !           186:                return;
        !           187:        }
        !           188: 
        !           189:        /*
        !           190:         * Remove us and execute next deferred function.
        !           191:         */
        !           192:        dmahead = dmahead->t_next;
        !           193:        spl( s );
        !           194:        (*dmahead->t_func)( dmahead->t_farg, dmahead );
        !           195: }
        !           196: 

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