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Annotation of coherent/d/286_KERNEL/USRSRC/286/dmalock.c, revision 1.1

1.1     ! root        1: /* $Header: /usr/src/sys/i8086/src/RCS/dmalock.c,v 1.1 89/06/30 16:21:26 src Exp $
        !             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        !            12:  *     An unpublished work by INETCO Systems, Ltd.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: src $
        !            19:  *
        !            20:  * $Creation: June 21, 1989 $
        !            21:  *
        !            22:  * $Log:       /usr/src/sys/i8086/src/RCS/dmalock.c,v $
        !            23:  * Revision 1.1        89/06/30  16:21:26      src
        !            24:  * Initial revision
        !            25:  * 
        !            26:  */
        !            27: 
        !            28: #include <sys/timeout.h>
        !            29: 
        !            30: typedef void (* vfp_t)();              /* Void function pointer type.       */
        !            31: 
        !            32: /*
        !            33:  * If the following variable is non-zero, DMA controller locking is enabled,
        !            34:  * allowing at access to only one DMA channel at a time.
        !            35:  */
        !            36: int DMALCK = 1;
        !            37: 
        !            38: static TIM * dmatail = (TIM *)0;       /* DMA deferred function queue tail. */
        !            39: static TIM * dmahead = (TIM *)0;       /* DMA deferred function queue head. */
        !            40: 
        !            41: /*
        !            42:  * int
        !            43:  * dmalock( dfp, fun, arg )
        !            44:  * TIM * dfp;
        !            45:  * vfp_t fun;
        !            46:  * int  arg;
        !            47:  *
        !            48:  *     Inputs: dfp  = Deferred function structure pointer.
        !            49:  *             fun  = Function to call if request is deferred.
        !            50:  *             arg  = Argument to pass to function.
        !            51:  *
        !            52:  *     Action: Either locks DMA controller immediately or defers function
        !            53:  *             call until lock can be granted.
        !            54:  *
        !            55:  *     Return: 0 = Lock granted or -1 = Lock deferred.
        !            56:  *
        !            57:  *     Notes:  DMA controller locking was introduced to cure a bug on the
        !            58:  *             NCR DMA controller, where overlapped DMA caused problems.
        !            59:  *             No action is taken if DMA locking is disabled.
        !            60:  */
        !            61: 
        !            62: int
        !            63: dmalock( dfp, fun, arg )
        !            64: register TIM  * dfp;
        !            65: vfp_t          fun;
        !            66: int            arg;
        !            67: {
        !            68:        register int s;         /* Interrupt mask state. */
        !            69: 
        !            70:        /*
        !            71:         * If DMA locking is disabled, allow functions to proceed.
        !            72:         */
        !            73:        if ( DMALCK == 0 )
        !            74:                return( 0 );
        !            75: 
        !            76:        /*
        !            77:         * Record function and argument to be invoked upon dmaunlock.
        !            78:         */
        !            79:        dfp->t_func = fun;
        !            80:        dfp->t_farg = arg;
        !            81:        dfp->t_next = (TIM *)0;
        !            82: 
        !            83:        s = sphi();
        !            84: 
        !            85:        /*
        !            86:         * If the queue is empty, put our structure at the head.
        !            87:         */
        !            88:        if ( dmahead == (TIM *)0 ) {
        !            89:                dmahead = dfp;
        !            90:                dmatail = dfp;
        !            91:                spl( s );
        !            92:                return( 0 );
        !            93:        }
        !            94: 
        !            95:        /*
        !            96:         * PARANOIA:    If our structure is already at the head of the queue,
        !            97:         *              print a message and return.
        !            98:         */
        !            99:        if ( dmahead == dfp ) {
        !           100:                spl( s );
        !           101:                printf( "dmalock: driver attempting to doubly lock DMA controller.\n" );
        !           102:                return( 0 );
        !           103:        }
        !           104: 
        !           105:        /*
        !           106:         * Append to tail of DMA deferred function queue.
        !           107:         */
        !           108:        dmatail->t_next = dfp;
        !           109:        dmatail         = dfp;
        !           110:        spl( s );
        !           111:        return( -1 );
        !           112: }
        !           113: 
        !           114: /*
        !           115:  * void
        !           116:  * dmaunlock( dfp )
        !           117:  * TIM * dfp;
        !           118:  *
        !           119:  *     Inputs: dfp = Deferred function structure pointer.
        !           120:  *
        !           121:  *     Action: Unlocks the DMA controller and calls the next deferred
        !           122:  *             function, if any.
        !           123:  *
        !           124:  *     Notes:  No action is taken if the deferred function structure pointer
        !           125:  *             is not the same as the one used to lock the DMA controller.
        !           126:  */
        !           127: 
        !           128: void
        !           129: dmaunlock( dfp )
        !           130: register TIM * dfp;
        !           131: {
        !           132:        register TIM *  qp;     /* Temporary function queue pointer.    */
        !           133:        register int    s;      /* Interrupt mask state.                */
        !           134: 
        !           135:        s = sphi();
        !           136: 
        !           137:        /*
        !           138:         * If the DMA controller is not locked, return.
        !           139:         */
        !           140:        if ( dmahead == (TIM *)0 ) {
        !           141:                spl( s );
        !           142:                return;
        !           143:        }
        !           144: 
        !           145:        /*
        !           146:         * If our lock is not the one holding the DMA controller:
        !           147:         */
        !           148:        if ( dmahead != dfp ) {
        !           149: 
        !           150:                /*
        !           151:                 * Look for us in queue.
        !           152:                 */
        !           153:                for ( qp = dmahead; qp != dmatail; qp = qp->t_next )
        !           154: 
        !           155:                        /*
        !           156:                         * If found, remove us.
        !           157:                         */
        !           158:                        if ( qp->t_next == dfp ) {
        !           159:                                qp->t_next = dfp->t_next;
        !           160: 
        !           161:                                if ( dmatail == dfp )
        !           162:                                        dmatail = qp;
        !           163: 
        !           164:                                break;
        !           165:                        }
        !           166: 
        !           167:                spl( s );
        !           168:                return;
        !           169:        }
        !           170: 
        !           171:        /*
        !           172:         * If there are no functions waiting for us, empty queue and return.
        !           173:         */
        !           174:        if ( dmahead == dmatail ) {
        !           175:                dmahead = (TIM *)0;
        !           176:                spl( s );
        !           177:                return;
        !           178:        }
        !           179: 
        !           180:        /*
        !           181:         * Remove us and execute next deferred function.
        !           182:         */
        !           183:        dmahead = dmahead->t_next;
        !           184:        spl( s );
        !           185:        (*dmahead->t_func)( dmahead->t_farg, dmahead );
        !           186: }
        !           187: 

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