scsi_merge.c

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/*
 *  scsi_merge.c Copyright (C) 1999 Eric Youngdale
 *
 *  SCSI queueing library.
 *      Initial versions: Eric Youngdale ([e-mail]).
 *                        Based upon conversations with large numbers
 *                        of people at Linux Expo.
 *	Support for dynamic DMA mapping: Jakub Jelinek ([e-mail]).
 */

/*
 * This file contains queue management functions that are used by SCSI.
 * Typically this is used for several purposes.   First, we need to ensure
 * that commands do not grow so large that they cannot be handled all at
 * once by a host adapter.   The various flavors of merge functions included
 * here serve this purpose.
 *
 * Note that it would be quite trivial to allow the low-level driver the
 * flexibility to define it's own queue handling functions.  For the time
 * being, the hooks are not present.   Right now we are just using the
 * data in the host template as an indicator of how we should be handling
 * queues, and we select routines that are optimized for that purpose.
 *
 * Some hosts do not impose any restrictions on the size of a request.
 * In such cases none of the merge functions in this file are called,
 * and we allow ll_rw_blk to merge requests in the default manner.
 * This isn't guaranteed to be optimal, but it should be pretty darned
 * good.   If someone comes up with ideas of better ways of managing queues
 * to improve on the default behavior, then certainly fit it into this
 * scheme in whatever manner makes the most sense.   Please note that
 * since each device has it's own queue, we have considerable flexibility
 * in queue management.
 */

#define __NO_VERSION__
#include <linux/config.h>
#include <linux/module.h>

#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/string.h>
#include <linux/malloc.h>
#include <linux/ioport.h>
#include <linux/kernel.h>
#include <linux/stat.h>
#include <linux/blk.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <linux/smp_lock.h>


#define __KERNEL_SYSCALLS__

#include <linux/unistd.h>

#include <asm/system.h>
#include <asm/irq.h>
#include <asm/dma.h>
#include <asm/io.h>

#include "scsi.h"
#include "hosts.h"
#include "constants.h"
#include <scsi/scsi_ioctl.h>

/*
 * This means that bounce buffers cannot be allocated in chunks > PAGE_SIZE.
 * Ultimately we should get away from using a dedicated DMA bounce buffer
 * pool, and we should instead try and use kmalloc() instead.  If we can
 * eliminate this pool, then this restriction would no longer be needed.
 */
#define DMA_SEGMENT_SIZE_LIMITED

#ifdef CONFIG_SCSI_DEBUG_QUEUES
/*
 * Enable a bunch of additional consistency checking.   Turn this off
 * if you are benchmarking.
 */
static int dump_stats(struct request *req,
		      int use_clustering,
		      int dma_host,
		      int segments)
{
	struct buffer_head *bh;

	/*
	 * Dump the information that we have.  We know we have an
	 * inconsistency.
	 */
	printk("nr_segments is %x\n", req->nr_segments);
	printk("counted segments is %x\n", segments);
	printk("Flags %d %d\n", use_clustering, dma_host);
	for (bh = req->bh; bh->b_reqnext != NULL; bh = bh->b_reqnext) 
	{
		printk("Segment 0x%p, blocks %d, addr 0x%lx\n",
		       bh,
		       bh->b_size >> 9,
		       virt_to_phys(bh->b_data - 1));
	}
	panic("Ththththaats all folks.  Too dangerous to continue.\n");
}


/*
 * Simple sanity check that we will use for the first go around
 * in order to ensure that we are doing the counting correctly.
 * This can be removed for optimization.
 */
#define SANITY_CHECK(req, _CLUSTER, _DMA)				\
    if( req->nr_segments != __count_segments(req, _CLUSTER, _DMA, NULL) )	\
    {									\
	printk("Incorrect segment count at 0x%p", current_text_addr());	\
	dump_stats(req, _CLUSTER, _DMA, __count_segments(req, _CLUSTER, _DMA, NULL)); \
    }
#else
#define SANITY_CHECK(req, _CLUSTER, _DMA)
#endif

static void dma_exhausted(Scsi_Cmnd * SCpnt, int i)
{
	int jj;
	struct scatterlist *sgpnt;
	int consumed = 0;

	sgpnt = (struct scatterlist *) SCpnt->request_buffer;

	/*
	 * Now print out a bunch of stats.  First, start with the request
	 * size.
	 */
	printk("dma_free_sectors:%d\n", scsi_dma_free_sectors);
	printk("use_sg:%d\ti:%d\n", SCpnt->use_sg, i);
	printk("request_bufflen:%d\n", SCpnt->request_bufflen);
	/*
	 * Now dump the scatter-gather table, up to the point of failure.
	 */
	for(jj=0; jj < SCpnt->use_sg; jj++)
	{
		printk("[%d]\tlen:%d\taddr:%p\talt:%p\n",
		       jj,
		       sgpnt[jj].length,
		       sgpnt[jj].address,
		       sgpnt[jj].alt_address);		       
		if( sgpnt[jj].alt_address != NULL )
		{
			consumed = (sgpnt[jj].length >> 9);
		}
	}
	printk("Total %d sectors consumed\n", consumed);
	panic("DMA pool exhausted");
}

/*
 * FIXME(eric) - the original disk code disabled clustering for MOD
 * devices.  I have no idea why we thought this was a good idea - my
 * guess is that it was an attempt to limit the size of requests to MOD
 * devices.
 */
#define CLUSTERABLE_DEVICE(SH,SD) (SH->use_clustering && \
				   SD->type != TYPE_MOD)

/*
 * This entire source file deals with the new queueing code.
 */

/*
 * Function:    __count_segments()
 *
 * Purpose:     Prototype for queue merge function.
 *
 * Arguments:   q       - Queue for which we are merging request.
 *              req     - request into which we wish to merge.
 *              use_clustering - 1 if this host wishes to use clustering
 *              dma_host - 1 if this host has ISA DMA issues (bus doesn't
 *                      expose all of the address lines, so that DMA cannot
 *                      be done from an arbitrary address).
 *		remainder - used to track the residual size of the last
 *			segment.  Comes in handy when we want to limit the 
 *			size of bounce buffer segments to PAGE_SIZE.
 *
 * Returns:     Count of the number of SG segments for the request.
 *
 * Lock status: 
 *
 * Notes:       This is only used for diagnostic purposes.
 */
__inline static int __count_segments(struct request *req,
				     int use_clustering,
				     int dma_host,
				     int * remainder)
{
	int ret = 1;
	int reqsize = 0;
	struct buffer_head *bh;
	struct buffer_head *bhnext;

	if( remainder != NULL ) {
		reqsize = *remainder;
	}

	/*
	 * Add in the size increment for the first buffer.
	 */
	bh = req->bh;
#ifdef DMA_SEGMENT_SIZE_LIMITED
	if( reqsize + bh->b_size > PAGE_SIZE ) {
		ret++;
		reqsize = bh->b_size;
	} else {
		reqsize += bh->b_size;
	}
#else
	reqsize += bh->b_size;
#endif

	for (bh = req->bh, bhnext = bh->b_reqnext; 
	     bhnext != NULL; 
	     bh = bhnext, bhnext = bh->b_reqnext) {
		if (use_clustering) {
			/* 
			 * See if we can do this without creating another
			 * scatter-gather segment.  In the event that this is a
			 * DMA capable host, make sure that a segment doesn't span
			 * the DMA threshold boundary.  
			 */
			if (dma_host &&
			    virt_to_phys(bhnext->b_data) - 1 == ISA_DMA_THRESHOLD) {
				ret++;
				reqsize = bhnext->b_size;
			} else if (CONTIGUOUS_BUFFERS(bh, bhnext)) {
				/*
				 * This one is OK.  Let it go.
				 */ 
#ifdef DMA_SEGMENT_SIZE_LIMITED
				/* Note scsi_malloc is only able to hand out
				 * chunks of memory in sizes of PAGE_SIZE or
				 * less.  Thus we need to keep track of
				 * the size of the piece that we have
				 * seen so far, and if we have hit
				 * the limit of PAGE_SIZE, then we are
				 * kind of screwed and we need to start
				 * another segment.
				 */
				if( dma_host
				    && virt_to_phys(bh->b_data) - 1 >= ISA_DMA_THRESHOLD
				    && reqsize + bhnext->b_size > PAGE_SIZE )
				{
					ret++;
					reqsize = bhnext->b_size;
					continue;
				}
#endif
				reqsize += bhnext->b_size;
				continue;
			}
			ret++;
			reqsize = bhnext->b_size;
		} else {
			ret++;
			reqsize = bhnext->b_size;
		}
	}
	if( remainder != NULL ) {
		*remainder = reqsize;
	}
	return ret;
}

/*
 * Function:    recount_segments()
 *
 * Purpose:     Recount the number of scatter-gather segments for this request.
 *
 * Arguments:   req     - request that needs recounting.
 *
 * Returns:     Count of the number of SG segments for the request.
 *
 * Lock status: Irrelevant.
 *
 * Notes:	This is only used when we have partially completed requests
 *		and the bit that is leftover is of an indeterminate size.
 *		This can come up if you get a MEDIUM_ERROR, for example,
 *		as we will have "completed" all of the sectors up to and
 *		including the bad sector, and the leftover bit is what
 *		we have to do now.  This tends to be a rare occurrence, so
 *		we aren't busting our butts to instantiate separate versions
 *		of this function for the 4 different flag values.  We
 *		probably should, however.
 */
void
recount_segments(Scsi_Cmnd * SCpnt)
{
	struct request *req;
	struct Scsi_Host *SHpnt;
	Scsi_Device * SDpnt;

	req   = &SCpnt->request;
	SHpnt = SCpnt->host;
	SDpnt = SCpnt->device;

	req->nr_segments = __count_segments(req, 
					    CLUSTERABLE_DEVICE(SHpnt, SDpnt),
					    SHpnt->unchecked_isa_dma, NULL);
}

#define MERGEABLE_BUFFERS(X,Y) \
(((((long)(X)->b_data+(X)->b_size)|((long)(Y)->b_data)) & \
  (DMA_CHUNK_SIZE - 1)) == 0)

#ifdef DMA_CHUNK_SIZE
static inline int scsi_new_mergeable(request_queue_t * q,
				     struct request * req,
				     struct Scsi_Host *SHpnt,
				     int max_segments)
{
	/*
	 * pci_map_sg will be able to merge these two
	 * into a single hardware sg entry, check if
	 * we'll have enough memory for the sg list.
	 * scsi.c allocates for this purpose
	 * min(64,sg_tablesize) entries.
	 */
	if (req->nr_segments >= max_segments ||
	    req->nr_segments >= SHpnt->sg_tablesize)
		return 0;
	req->nr_segments++;
	q->elevator.nr_segments++;
	return 1;
}

static inline int scsi_new_segment(request_queue_t * q,
				   struct request * req,
				   struct Scsi_Host *SHpnt,
				   int max_segments)
{
	/*
	 * pci_map_sg won't be able to map these two
	 * into a single hardware sg entry, so we have to
	 * check if things fit into sg_tablesize.
	 */
	if (req->nr_hw_segments >= SHpnt->sg_tablesize ||
	     req->nr_segments >= SHpnt->sg_tablesize)
		return 0;
	if (req->nr_segments >= max_segments)
		return 0;
	req->nr_hw_segments++;
	req->nr_segments++;
	q->elevator.nr_segments++;
	return 1;
}
#else
static inline int scsi_new_segment(request_queue_t * q,
				   struct request * req,
				   struct Scsi_Host *SHpnt,
				   int max_segments)
{
	if (req->nr_segments < SHpnt->sg_tablesize &&
	    req->nr_segments < max_segments) {
		/*
		 * This will form the start of a new segment.  Bump the 
		 * counter.
		 */
		req->nr_segments++;
		q->elevator.nr_segments++;
		return 1;
	} else {
		return 0;
	}
}
#endif

/*
 * Function:    __scsi_merge_fn()
 *
 * Purpose:     Prototype for queue merge function.
 *
 * Arguments:   q       - Queue for which we are merging request.
 *              req     - request into which we wish to merge.
 *              bh      - Block which we may wish to merge into request
 *              use_clustering - 1 if this host wishes to use clustering
 *              dma_host - 1 if this host has ISA DMA issues (bus doesn't
 *                      expose all of the address lines, so that DMA cannot
 *                      be done from an arbitrary address).
 *
 * Returns:     1 if it is OK to merge the block into the request.  0