/*++

Copyright (c) 1991  Microsoft Corporation

Module Name:

    j4flshio.c

Abstract:


    This module implements the system dependent kernel function to flush
    the data cache for I/O transfers on a MIPS R4000 Jazz system.

Author:

    David N. Cutler (davec) 24-Apr-1991

Environment:

    Kernel mode only.

Revision History:

--*/

#include "halp.h"


VOID
HalFlushIoBuffers (
    IN PMDL Mdl,
    IN BOOLEAN ReadOperation,
    IN BOOLEAN DmaOperation
    )

/*++

Routine Description:

    This function flushes the I/O buffer specified by the memory descriptor
    list from the data cache on the current processor.

Arguments:

    Mdl - Supplies a pointer to a memory descriptor list that describes the
        I/O buffer location.

    ReadOperation - Supplies a boolean value that determines whether the I/O
        operation is a read into memory.

    DmaOperation - Supplies a boolean value that determines whether the I/O
        operation is a DMA operation.

Return Value:

    None.

--*/

{

    ULONG  CacheSegment;
    ULONG  Length;
    ULONG  Offset;
    KIRQL  OldIrql;
    PULONG PageFrame;
    ULONG  Source;

    //
    // The Jazz R4000 uses a write back data cache and, therefore, must be
    // flushed on reads and writes.
    //
    // If the length of the I/O operation is greater than the size of the
    // data cache, then sweep the entire data cache. Otherwise, export or
    // purge individual pages from the data cache as appropriate.
    //

    Offset = Mdl->ByteOffset & PCR->DcacheAlignment;
    Length = (Mdl->ByteCount +
                        PCR->DcacheAlignment + Offset) & ~PCR->DcacheAlignment;


    if ((Length > PCR->FirstLevelDcacheSize) &&
        (Length > PCR->SecondLevelDcacheSize)) {

        if ((ReadOperation != FALSE) &&
            ((Mdl->MdlFlags & MDL_IO_PAGE_READ) != 0)) {
            HalSweepDcache();
            HalSweepIcache();
        }

    } else {

        //
        // Export or purge the specified pages from the data cache and
        // instruction caches as appropriate.
        //
        // Compute the number of pages to flush and the starting MDL page
        // frame address.
        //

        Offset = Mdl->ByteOffset & ~PCR->DcacheAlignment;
        PageFrame = (PULONG)(Mdl + 1);
        Source = ((ULONG)(Mdl->StartVa) & 0xfffff000) | Offset;

        //
        // Export or purge the specified page segments from the data and
        // instruction caches as appropriate.
        //

        do {

            if (Length >= (PAGE_SIZE - Offset)) {
                CacheSegment = PAGE_SIZE - Offset;
            } else {
                CacheSegment = Length;
            }

            if (ReadOperation == TRUE) {
              if (DmaOperation == FALSE) {
                if ((Mdl->MdlFlags & MDL_IO_PAGE_READ) != 0) {
                  HalFlushDcachePage((PVOID)Source, *PageFrame, CacheSegment);
                }
              }
              if ((Mdl->MdlFlags & MDL_IO_PAGE_READ) != 0) {
                  HalPurgeIcachePage((PVOID)Source, *PageFrame, CacheSegment);
              }
            }

            PageFrame += 1;
            Length -= CacheSegment;
            Offset = 0;
            Source += CacheSegment;

        } while(Length != 0);
    }
    return;
}

ULONG
HalGetDmaAlignmentRequirement (
    VOID
    )

/*++

Routine Description:

    This function returns the alignment requirements for DMA transfers on
    host system.

Arguments:

    None.

Return Value:

    The DMA alignment requirement is returned as the fucntion value.

--*/

{

    return PCR->DcacheFillSize;
}