Commit f94b533d authored by Tom Tucker's avatar Tom Tucker Committed by Roland Dreier

RDMA/amso1100: Add driver for Ammasso 1100 RNIC

Add a driver for the Ammasso 1100 gigabit ethernet RNIC.
Signed-off-by: default avatarTom Tucker <tom@opengridcomputing.com>
Signed-off-by: default avatarSteve Wise <swise@opengridcomputing.com>
Signed-off-by: default avatarRoland Dreier <rolandd@cisco.com>
parent 07ebafba
......@@ -298,6 +298,14 @@ L: info-linux@geode.amd.com
W: http://www.amd.com/us-en/ConnectivitySolutions/TechnicalResources/0,,50_2334_2452_11363,00.html
S: Supported
AMSO1100 RNIC DRIVER
P: Tom Tucker
M: tom@opengridcomputing.com
P: Steve Wise
M: swise@opengridcomputing.com
L: openib-general@openib.org
S: Maintained
AOA (Apple Onboard Audio) ALSA DRIVER
P: Johannes Berg
M: johannes@sipsolutions.net
......
......@@ -37,6 +37,7 @@ config INFINIBAND_ADDR_TRANS
source "drivers/infiniband/hw/mthca/Kconfig"
source "drivers/infiniband/hw/ipath/Kconfig"
source "drivers/infiniband/hw/ehca/Kconfig"
source "drivers/infiniband/hw/amso1100/Kconfig"
source "drivers/infiniband/ulp/ipoib/Kconfig"
......
......@@ -2,6 +2,7 @@ obj-$(CONFIG_INFINIBAND) += core/
obj-$(CONFIG_INFINIBAND_MTHCA) += hw/mthca/
obj-$(CONFIG_INFINIBAND_IPATH) += hw/ipath/
obj-$(CONFIG_INFINIBAND_EHCA) += hw/ehca/
obj-$(CONFIG_INFINIBAND_AMSO1100) += hw/amso1100/
obj-$(CONFIG_INFINIBAND_IPOIB) += ulp/ipoib/
obj-$(CONFIG_INFINIBAND_SRP) += ulp/srp/
obj-$(CONFIG_INFINIBAND_ISER) += ulp/iser/
ifdef CONFIG_INFINIBAND_AMSO1100_DEBUG
EXTRA_CFLAGS += -DDEBUG
endif
obj-$(CONFIG_INFINIBAND_AMSO1100) += iw_c2.o
iw_c2-y := c2.o c2_provider.o c2_rnic.o c2_alloc.o c2_mq.o c2_ae.o c2_vq.o \
c2_intr.o c2_cq.o c2_qp.o c2_cm.o c2_mm.o c2_pd.o
config INFINIBAND_AMSO1100
tristate "Ammasso 1100 HCA support"
depends on PCI && INET && INFINIBAND
---help---
This is a low-level driver for the Ammasso 1100 host
channel adapter (HCA).
config INFINIBAND_AMSO1100_DEBUG
bool "Verbose debugging output"
depends on INFINIBAND_AMSO1100
default n
---help---
This option causes the amso1100 driver to produce a bunch of
debug messages. Select this if you are developing the driver
or trying to diagnose a problem.
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/*
* Copyright (c) 2005 Ammasso, Inc. All rights reserved.
* Copyright (c) 2005 Open Grid Computing, Inc. All rights reserved.
*
* This software is available to you under a choice of one of two
* licenses. You may choose to be licensed under the terms of the GNU
* General Public License (GPL) Version 2, available from the file
* COPYING in the main directory of this source tree, or the
* OpenIB.org BSD license below:
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above
* copyright notice, this list of conditions and the following
* disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials
* provided with the distribution.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "c2.h"
#include <rdma/iw_cm.h>
#include "c2_status.h"
#include "c2_ae.h"
static int c2_convert_cm_status(u32 c2_status)
{
switch (c2_status) {
case C2_CONN_STATUS_SUCCESS:
return 0;
case C2_CONN_STATUS_REJECTED:
return -ENETRESET;
case C2_CONN_STATUS_REFUSED:
return -ECONNREFUSED;
case C2_CONN_STATUS_TIMEDOUT:
return -ETIMEDOUT;
case C2_CONN_STATUS_NETUNREACH:
return -ENETUNREACH;
case C2_CONN_STATUS_HOSTUNREACH:
return -EHOSTUNREACH;
case C2_CONN_STATUS_INVALID_RNIC:
return -EINVAL;
case C2_CONN_STATUS_INVALID_QP:
return -EINVAL;
case C2_CONN_STATUS_INVALID_QP_STATE:
return -EINVAL;
case C2_CONN_STATUS_ADDR_NOT_AVAIL:
return -EADDRNOTAVAIL;
default:
printk(KERN_ERR PFX
"%s - Unable to convert CM status: %d\n",
__FUNCTION__, c2_status);
return -EIO;
}
}
#ifdef DEBUG
static const char* to_event_str(int event)
{
static const char* event_str[] = {
"CCAE_REMOTE_SHUTDOWN",
"CCAE_ACTIVE_CONNECT_RESULTS",
"CCAE_CONNECTION_REQUEST",
"CCAE_LLP_CLOSE_COMPLETE",
"CCAE_TERMINATE_MESSAGE_RECEIVED",
"CCAE_LLP_CONNECTION_RESET",
"CCAE_LLP_CONNECTION_LOST",
"CCAE_LLP_SEGMENT_SIZE_INVALID",
"CCAE_LLP_INVALID_CRC",
"CCAE_LLP_BAD_FPDU",
"CCAE_INVALID_DDP_VERSION",
"CCAE_INVALID_RDMA_VERSION",
"CCAE_UNEXPECTED_OPCODE",
"CCAE_INVALID_DDP_QUEUE_NUMBER",
"CCAE_RDMA_READ_NOT_ENABLED",
"CCAE_RDMA_WRITE_NOT_ENABLED",
"CCAE_RDMA_READ_TOO_SMALL",
"CCAE_NO_L_BIT",
"CCAE_TAGGED_INVALID_STAG",
"CCAE_TAGGED_BASE_BOUNDS_VIOLATION",
"CCAE_TAGGED_ACCESS_RIGHTS_VIOLATION",
"CCAE_TAGGED_INVALID_PD",
"CCAE_WRAP_ERROR",
"CCAE_BAD_CLOSE",
"CCAE_BAD_LLP_CLOSE",
"CCAE_INVALID_MSN_RANGE",
"CCAE_INVALID_MSN_GAP",
"CCAE_IRRQ_OVERFLOW",
"CCAE_IRRQ_MSN_GAP",
"CCAE_IRRQ_MSN_RANGE",
"CCAE_IRRQ_INVALID_STAG",
"CCAE_IRRQ_BASE_BOUNDS_VIOLATION",
"CCAE_IRRQ_ACCESS_RIGHTS_VIOLATION",
"CCAE_IRRQ_INVALID_PD",
"CCAE_IRRQ_WRAP_ERROR",
"CCAE_CQ_SQ_COMPLETION_OVERFLOW",
"CCAE_CQ_RQ_COMPLETION_ERROR",
"CCAE_QP_SRQ_WQE_ERROR",
"CCAE_QP_LOCAL_CATASTROPHIC_ERROR",
"CCAE_CQ_OVERFLOW",
"CCAE_CQ_OPERATION_ERROR",
"CCAE_SRQ_LIMIT_REACHED",
"CCAE_QP_RQ_LIMIT_REACHED",
"CCAE_SRQ_CATASTROPHIC_ERROR",
"CCAE_RNIC_CATASTROPHIC_ERROR"
};
if (event < CCAE_REMOTE_SHUTDOWN ||
event > CCAE_RNIC_CATASTROPHIC_ERROR)
return "<invalid event>";
event -= CCAE_REMOTE_SHUTDOWN;
return event_str[event];
}
static const char *to_qp_state_str(int state)
{
switch (state) {
case C2_QP_STATE_IDLE:
return "C2_QP_STATE_IDLE";
case C2_QP_STATE_CONNECTING:
return "C2_QP_STATE_CONNECTING";
case C2_QP_STATE_RTS:
return "C2_QP_STATE_RTS";
case C2_QP_STATE_CLOSING:
return "C2_QP_STATE_CLOSING";
case C2_QP_STATE_TERMINATE:
return "C2_QP_STATE_TERMINATE";
case C2_QP_STATE_ERROR:
return "C2_QP_STATE_ERROR";
default:
return "<invalid QP state>";
};
}
#endif
void c2_ae_event(struct c2_dev *c2dev, u32 mq_index)
{
struct c2_mq *mq = c2dev->qptr_array[mq_index];
union c2wr *wr;
void *resource_user_context;
struct iw_cm_event cm_event;
struct ib_event ib_event;
enum c2_resource_indicator resource_indicator;
enum c2_event_id event_id;
unsigned long flags;
int status;
/*
* retreive the message
*/
wr = c2_mq_consume(mq);
if (!wr)
return;
memset(&ib_event, 0, sizeof(ib_event));
memset(&cm_event, 0, sizeof(cm_event));
event_id = c2_wr_get_id(wr);
resource_indicator = be32_to_cpu(wr->ae.ae_generic.resource_type);
resource_user_context =
(void *) (unsigned long) wr->ae.ae_generic.user_context;
status = cm_event.status = c2_convert_cm_status(c2_wr_get_result(wr));
pr_debug("event received c2_dev=%p, event_id=%d, "
"resource_indicator=%d, user_context=%p, status = %d\n",
c2dev, event_id, resource_indicator, resource_user_context,
status);
switch (resource_indicator) {
case C2_RES_IND_QP:{
struct c2_qp *qp = (struct c2_qp *)resource_user_context;
struct iw_cm_id *cm_id = qp->cm_id;
struct c2wr_ae_active_connect_results *res;
if (!cm_id) {
pr_debug("event received, but cm_id is <nul>, qp=%p!\n",
qp);
goto ignore_it;
}
pr_debug("%s: event = %s, user_context=%llx, "
"resource_type=%x, "
"resource=%x, qp_state=%s\n",
__FUNCTION__,
to_event_str(event_id),
be64_to_cpu(wr->ae.ae_generic.user_context),
be32_to_cpu(wr->ae.ae_generic.resource_type),
be32_to_cpu(wr->ae.ae_generic.resource),
to_qp_state_str(be32_to_cpu(wr->ae.ae_generic.qp_state)));
c2_set_qp_state(qp, be32_to_cpu(wr->ae.ae_generic.qp_state));
switch (event_id) {
case CCAE_ACTIVE_CONNECT_RESULTS:
res = &wr->ae.ae_active_connect_results;
cm_event.event = IW_CM_EVENT_CONNECT_REPLY;
cm_event.local_addr.sin_addr.s_addr = res->laddr;
cm_event.remote_addr.sin_addr.s_addr = res->raddr;
cm_event.local_addr.sin_port = res->lport;
cm_event.remote_addr.sin_port = res->rport;
if (status == 0) {
cm_event.private_data_len =
be32_to_cpu(res->private_data_length);
cm_event.private_data = res->private_data;
} else {
spin_lock_irqsave(&qp->lock, flags);
if (qp->cm_id) {
qp->cm_id->rem_ref(qp->cm_id);
qp->cm_id = NULL;
}
spin_unlock_irqrestore(&qp->lock, flags);
cm_event.private_data_len = 0;
cm_event.private_data = NULL;
}
if (cm_id->event_handler)
cm_id->event_handler(cm_id, &cm_event);
break;
case CCAE_TERMINATE_MESSAGE_RECEIVED:
case CCAE_CQ_SQ_COMPLETION_OVERFLOW:
ib_event.device = &c2dev->ibdev;
ib_event.element.qp = &qp->ibqp;
ib_event.event = IB_EVENT_QP_REQ_ERR;
if (qp->ibqp.event_handler)
qp->ibqp.event_handler(&ib_event,
qp->ibqp.
qp_context);
break;
case CCAE_BAD_CLOSE:
case CCAE_LLP_CLOSE_COMPLETE:
case CCAE_LLP_CONNECTION_RESET:
case CCAE_LLP_CONNECTION_LOST:
BUG_ON(cm_id->event_handler==(void*)0x6b6b6b6b);
spin_lock_irqsave(&qp->lock, flags);
if (qp->cm_id) {
qp->cm_id->rem_ref(qp->cm_id);
qp->cm_id = NULL;
}
spin_unlock_irqrestore(&qp->lock, flags);
cm_event.event = IW_CM_EVENT_CLOSE;
cm_event.status = 0;
if (cm_id->event_handler)
cm_id->event_handler(cm_id, &cm_event);
break;
default:
BUG_ON(1);
pr_debug("%s:%d Unexpected event_id=%d on QP=%p, "
"CM_ID=%p\n",
__FUNCTION__, __LINE__,
event_id, qp, cm_id);
break;
}
break;
}
case C2_RES_IND_EP:{
struct c2wr_ae_connection_request *req =
&wr->ae.ae_connection_request;
struct iw_cm_id *cm_id =
(struct iw_cm_id *)resource_user_context;
pr_debug("C2_RES_IND_EP event_id=%d\n", event_id);
if (event_id != CCAE_CONNECTION_REQUEST) {
pr_debug("%s: Invalid event_id: %d\n",
__FUNCTION__, event_id);
break;
}
cm_event.event = IW_CM_EVENT_CONNECT_REQUEST;
cm_event.provider_data = (void*)(unsigned long)req->cr_handle;
cm_event.local_addr.sin_addr.s_addr = req->laddr;
cm_event.remote_addr.sin_addr.s_addr = req->raddr;
cm_event.local_addr.sin_port = req->lport;
cm_event.remote_addr.sin_port = req->rport;
cm_event.private_data_len =
be32_to_cpu(req->private_data_length);
cm_event.private_data = req->private_data;
if (cm_id->event_handler)
cm_id->event_handler(cm_id, &cm_event);
break;
}
case C2_RES_IND_CQ:{
struct c2_cq *cq =
(struct c2_cq *) resource_user_context;
pr_debug("IB_EVENT_CQ_ERR\n");
ib_event.device = &c2dev->ibdev;
ib_event.element.cq = &cq->ibcq;
ib_event.event = IB_EVENT_CQ_ERR;
if (cq->ibcq.event_handler)
cq->ibcq.event_handler(&ib_event,
cq->ibcq.cq_context);
}
default:
printk("Bad resource indicator = %d\n",
resource_indicator);
break;
}
ignore_it:
c2_mq_free(mq);
}
/*
* Copyright (c) 2005 Ammasso, Inc. All rights reserved.
* Copyright (c) 2005 Open Grid Computing, Inc. All rights reserved.
*
* This software is available to you under a choice of one of two
* licenses. You may choose to be licensed under the terms of the GNU
* General Public License (GPL) Version 2, available from the file
* COPYING in the main directory of this source tree, or the
* OpenIB.org BSD license below:
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above
* copyright notice, this list of conditions and the following
* disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials
* provided with the distribution.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#ifndef _C2_AE_H_
#define _C2_AE_H_
/*
* WARNING: If you change this file, also bump C2_IVN_BASE
* in common/include/clustercore/c2_ivn.h.
*/
/*
* Asynchronous Event Identifiers
*
* These start at 0x80 only so it's obvious from inspection that
* they are not work-request statuses. This isn't critical.
*
* NOTE: these event id's must fit in eight bits.
*/
enum c2_event_id {
CCAE_REMOTE_SHUTDOWN = 0x80,
CCAE_ACTIVE_CONNECT_RESULTS,
CCAE_CONNECTION_REQUEST,
CCAE_LLP_CLOSE_COMPLETE,
CCAE_TERMINATE_MESSAGE_RECEIVED,
CCAE_LLP_CONNECTION_RESET,
CCAE_LLP_CONNECTION_LOST,
CCAE_LLP_SEGMENT_SIZE_INVALID,
CCAE_LLP_INVALID_CRC,
CCAE_LLP_BAD_FPDU,
CCAE_INVALID_DDP_VERSION,
CCAE_INVALID_RDMA_VERSION,
CCAE_UNEXPECTED_OPCODE,
CCAE_INVALID_DDP_QUEUE_NUMBER,
CCAE_RDMA_READ_NOT_ENABLED,
CCAE_RDMA_WRITE_NOT_ENABLED,
CCAE_RDMA_READ_TOO_SMALL,
CCAE_NO_L_BIT,
CCAE_TAGGED_INVALID_STAG,
CCAE_TAGGED_BASE_BOUNDS_VIOLATION,
CCAE_TAGGED_ACCESS_RIGHTS_VIOLATION,
CCAE_TAGGED_INVALID_PD,
CCAE_WRAP_ERROR,
CCAE_BAD_CLOSE,
CCAE_BAD_LLP_CLOSE,
CCAE_INVALID_MSN_RANGE,
CCAE_INVALID_MSN_GAP,
CCAE_IRRQ_OVERFLOW,
CCAE_IRRQ_MSN_GAP,
CCAE_IRRQ_MSN_RANGE,
CCAE_IRRQ_INVALID_STAG,
CCAE_IRRQ_BASE_BOUNDS_VIOLATION,
CCAE_IRRQ_ACCESS_RIGHTS_VIOLATION,
CCAE_IRRQ_INVALID_PD,
CCAE_IRRQ_WRAP_ERROR,
CCAE_CQ_SQ_COMPLETION_OVERFLOW,
CCAE_CQ_RQ_COMPLETION_ERROR,
CCAE_QP_SRQ_WQE_ERROR,
CCAE_QP_LOCAL_CATASTROPHIC_ERROR,
CCAE_CQ_OVERFLOW,
CCAE_CQ_OPERATION_ERROR,
CCAE_SRQ_LIMIT_REACHED,
CCAE_QP_RQ_LIMIT_REACHED,
CCAE_SRQ_CATASTROPHIC_ERROR,
CCAE_RNIC_CATASTROPHIC_ERROR
/* WARNING If you add more id's, make sure their values fit in eight bits. */
};
/*
* Resource Indicators and Identifiers
*/
enum c2_resource_indicator {
C2_RES_IND_QP = 1,
C2_RES_IND_EP,
C2_RES_IND_CQ,
C2_RES_IND_SRQ,
};
#endif /* _C2_AE_H_ */
<
/*
* Copyright (c) 2004 Topspin Communications. All rights reserved.
* Copyright (c) 2005 Open Grid Computing, Inc. All rights reserved.
*
* This software is available to you under a choice of one of two
* licenses. You may choose to be licensed under the terms of the GNU
* General Public License (GPL) Version 2, available from the file
* COPYING in the main directory of this source tree, or the
* OpenIB.org BSD license below:
*
* Redistribution and use in source and binary forms, with or
* without modification, are permitted provided that the following
* conditions are met:
*
* - Redistributions of source code must retain the above
* copyright notice, this list of conditions and the following
* disclaimer.
*
* - Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following
* disclaimer in the documentation and/or other materials
* provided with the distribution.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/bitmap.h>
#include "c2.h"
static int c2_alloc_mqsp_chunk(struct c2_dev *c2dev, gfp_t gfp_mask,
struct sp_chunk **head)
{
int i;
struct sp_chunk *new_head;
new_head = (struct sp_chunk *) __get_free_page(gfp_mask);
if (new_head == NULL)
return -ENOMEM;
new_head->dma_addr = dma_map_single(c2dev->ibdev.dma_device, new_head,
PAGE_SIZE, DMA_FROM_DEVICE);
pci_unmap_addr_set(new_head, mapping, new_head->dma_addr);
new_head->next = NULL;
new_head->head = 0;
/* build list where each index is the next free slot */
for (i = 0;
i < (PAGE_SIZE - sizeof(struct sp_chunk) -
sizeof(u16)) / sizeof(u16) - 1;
i++) {
new_head->shared_ptr[i] = i + 1;
}
/* terminate list */
new_head->shared_ptr[i] = 0xFFFF;
*head = new_head;
return 0;
}
int c2_init_mqsp_pool(struct c2_dev *c2dev, gfp_t gfp_mask,
struct sp_chunk **root)
{
return c2_alloc_mqsp_chunk(c2dev, gfp_mask, root);
}
void c2_free_mqsp_pool(struct c2_dev *c2dev, struct sp_chunk *root)
{
struct sp_chunk *next;
while (root) {
next = root->next;
dma_unmap_single(c2dev->ibdev.dma_device,
pci_unmap_addr(root, mapping), PAGE_SIZE,
DMA_FROM_DEVICE);
__free_page((struct page *) root);
root = next;
}
}
u16 *c2_alloc_mqsp(struct c2_dev *c2dev, struct sp_chunk *head,
dma_addr_t *dma_addr, gfp_t gfp_mask)
{
u16 mqsp;
while (head) {
mqsp = head->head;
if (mqsp != 0xFFFF) {
head->head = head->shared_ptr[mqsp];
break;
} else if (head->next == NULL) {
if (c2_alloc_mqsp_chunk(c2dev, gfp_mask, &head->next) ==
0) {
head = head->next;
mqsp = head->head;
head->head = head->shared_ptr[mqsp];
break;
} else
return NULL;
} else
head = head->next;
}
if (head) {
*dma_addr = head->dma_addr +
((unsigned long) &(head->shared_ptr[mqsp]) -
(unsigned long) head);
pr_debug("%s addr %p dma_addr %llx\n", __FUNCTION__,
&(head->shared_ptr[mqsp]), (u64)*dma_addr);
return &(head->shared_ptr[mqsp]);
}
return NULL;
}
void c2_free_mqsp(u16 * mqsp)
{
struct sp_chunk *head;
u16 idx;
/* The chunk containing this ptr begins at the page boundary */
head = (struct sp_chunk *) ((unsigned long) mqsp & PAGE_MASK);
/* Link head to new mqsp */
*mqsp = head->head;
/* Compute the shared_ptr index */
idx = ((unsigned long) mqsp & ~PAGE_MASK) >> 1;
idx -= (unsigned long) &(((struct sp_chunk *) 0)->shared_ptr[0]) >> 1;
/* Point this index at the head */
head->shared_ptr[idx] = head->head;
/* Point head at this index */
head->head = idx;
}