Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030252AbWHQUNU (ORCPT ); Thu, 17 Aug 2006 16:13:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030255AbWHQULv (ORCPT ); Thu, 17 Aug 2006 16:11:51 -0400 Received: from sj-iport-2-in.cisco.com ([171.71.176.71]:20743 "EHLO sj-iport-2.cisco.com") by vger.kernel.org with ESMTP id S1030254AbWHQULE (ORCPT ); Thu, 17 Aug 2006 16:11:04 -0400 X-IronPort-AV: i="4.08,139,1154934000"; d="scan'208"; a="336821743:sNHT64337988" Cc: schihei@de.ibm.com, RAISCH@de.ibm.com, HNGUYEN@de.ibm.com, MEDER@de.ibm.com Subject: [PATCH 10/13] IB/ehca: hipz In-Reply-To: <20068171311.sHGelL4wOwoc17UG@cisco.com> X-Mailer: Roland's Patchbomber Date: Thu, 17 Aug 2006 13:11:02 -0700 Message-Id: <20068171311.jebQ3TFd5jvynHCW@cisco.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII To: openib-general@openib.org, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org Content-Transfer-Encoding: 7BIT From: Roland Dreier X-OriginalArrivalTime: 17 Aug 2006 20:11:02.0347 (UTC) FILETIME=[433A81B0:01C6C239] Authentication-Results: sj-dkim-2.cisco.com; header.From=rolandd@cisco.com; dkim=pass ( sig from cisco.com verified; ); Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 15943 Lines: 611 drivers/infiniband/hw/ehca/hipz_fns.h | 68 +++++ drivers/infiniband/hw/ehca/hipz_fns_core.h | 122 +++++++++ drivers/infiniband/hw/ehca/hipz_hw.h | 390 ++++++++++++++++++++++++++++ 3 files changed, 580 insertions(+), 0 deletions(-) diff --git a/drivers/infiniband/hw/ehca/hipz_fns.h b/drivers/infiniband/hw/ehca/hipz_fns.h new file mode 100644 index 0000000..9dac93d --- /dev/null +++ b/drivers/infiniband/hw/ehca/hipz_fns.h @@ -0,0 +1,68 @@ +/* + * IBM eServer eHCA Infiniband device driver for Linux on POWER + * + * HW abstraction register functions + * + * Authors: Christoph Raisch + * Reinhard Ernst + * + * Copyright (c) 2005 IBM Corporation + * + * All rights reserved. + * + * This source code is distributed under a dual license of GPL v2.0 and OpenIB + * BSD. + * + * OpenIB BSD License + * + * 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. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" + * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR + * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER + * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + */ + +#ifndef __HIPZ_FNS_H__ +#define __HIPZ_FNS_H__ + +#include "ehca_classes.h" +#include "hipz_hw.h" + +#include "hipz_fns_core.h" + +#define hipz_galpa_store_eq(gal, offset, value) \ + hipz_galpa_store(gal, EQTEMM_OFFSET(offset), value) + +#define hipz_galpa_load_eq(gal, offset) \ + hipz_galpa_load(gal, EQTEMM_OFFSET(offset)) + +#define hipz_galpa_store_qped(gal, offset, value) \ + hipz_galpa_store(gal, QPEDMM_OFFSET(offset), value) + +#define hipz_galpa_load_qped(gal, offset) \ + hipz_galpa_load(gal, QPEDMM_OFFSET(offset)) + +#define hipz_galpa_store_mrmw(gal, offset, value) \ + hipz_galpa_store(gal, MRMWMM_OFFSET(offset), value) + +#define hipz_galpa_load_mrmw(gal, offset) \ + hipz_galpa_load(gal, MRMWMM_OFFSET(offset)) + +#endif diff --git a/drivers/infiniband/hw/ehca/hipz_fns_core.h b/drivers/infiniband/hw/ehca/hipz_fns_core.h new file mode 100644 index 0000000..ff8d7ed --- /dev/null +++ b/drivers/infiniband/hw/ehca/hipz_fns_core.h @@ -0,0 +1,122 @@ +/* + * IBM eServer eHCA Infiniband device driver for Linux on POWER + * + * HW abstraction register functions + * + * Authors: Christoph Raisch + * Heiko J Schick + * Hoang-Nam Nguyen + * Reinhard Ernst + * + * Copyright (c) 2005 IBM Corporation + * + * All rights reserved. + * + * This source code is distributed under a dual license of GPL v2.0 and OpenIB + * BSD. + * + * OpenIB BSD License + * + * 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. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" + * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR + * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER + * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + */ + +#ifndef __HIPZ_FNS_CORE_H__ +#define __HIPZ_FNS_CORE_H__ + +#include "hcp_phyp.h" +#include "hipz_hw.h" + +#define hipz_galpa_store_cq(gal, offset, value) \ + hipz_galpa_store(gal, CQTEMM_OFFSET(offset), value) + +#define hipz_galpa_load_cq(gal, offset) \ + hipz_galpa_load(gal, CQTEMM_OFFSET(offset)) + +#define hipz_galpa_store_qp(gal,offset, value) \ + hipz_galpa_store(gal, QPTEMM_OFFSET(offset), value) +#define hipz_galpa_load_qp(gal, offset) \ + hipz_galpa_load(gal,QPTEMM_OFFSET(offset)) + +static inline void hipz_update_sqa(struct ehca_qp *qp, u16 nr_wqes) +{ + struct h_galpa gal; + + EDEB_EN(7, "qp=%p", qp); + gal = qp->galpas.kernel; + /* ringing doorbell :-) */ + hipz_galpa_store_qp(gal, qpx_sqa, EHCA_BMASK_SET(QPX_SQADDER, nr_wqes)); + EDEB_EX(7, "qp=%p QPx_SQA = %i", qp, nr_wqes); +} + +static inline void hipz_update_rqa(struct ehca_qp *qp, u16 nr_wqes) +{ + struct h_galpa gal; + + EDEB_EN(7, "qp=%p", qp); + gal = qp->galpas.kernel; + /* ringing doorbell :-) */ + hipz_galpa_store_qp(gal, qpx_rqa, EHCA_BMASK_SET(QPX_RQADDER, nr_wqes)); + EDEB_EX(7, "qp=%p QPx_RQA = %i", qp, nr_wqes); +} + +static inline void hipz_update_feca(struct ehca_cq *cq, u32 nr_cqes) +{ + struct h_galpa gal; + + EDEB_EN(7, "cq=%p", cq); + gal = cq->galpas.kernel; + hipz_galpa_store_cq(gal, cqx_feca, + EHCA_BMASK_SET(CQX_FECADDER, nr_cqes)); + EDEB_EX(7, "cq=%p CQx_FECA = %i", cq, nr_cqes); +} + +static inline void hipz_set_cqx_n0(struct ehca_cq *cq, u32 value) +{ + struct h_galpa gal; + u64 CQx_N0_reg = 0; + + EDEB_EN(7, "cq=%p event on solicited completion -- write CQx_N0", cq); + gal = cq->galpas.kernel; + hipz_galpa_store_cq(gal, cqx_n0, + EHCA_BMASK_SET(CQX_N0_GENERATE_SOLICITED_COMP_EVENT, + value)); + CQx_N0_reg = hipz_galpa_load_cq(gal, cqx_n0); + EDEB_EX(7, "cq=%p loaded CQx_N0=%lx", cq, (unsigned long)CQx_N0_reg); +} + +static inline void hipz_set_cqx_n1(struct ehca_cq *cq, u32 value) +{ + struct h_galpa gal; + u64 CQx_N1_reg = 0; + + EDEB_EN(7, "cq=%p event on completion -- write CQx_N1", + cq); + gal = cq->galpas.kernel; + hipz_galpa_store_cq(gal, cqx_n1, + EHCA_BMASK_SET(CQX_N1_GENERATE_COMP_EVENT, value)); + CQx_N1_reg = hipz_galpa_load_cq(gal, cqx_n1); + EDEB_EX(7, "cq=%p loaded CQx_N1=%lx", cq, (unsigned long)CQx_N1_reg); +} + +#endif /* __HIPZ_FNC_CORE_H__ */ diff --git a/drivers/infiniband/hw/ehca/hipz_hw.h b/drivers/infiniband/hw/ehca/hipz_hw.h new file mode 100644 index 0000000..f5f4871 --- /dev/null +++ b/drivers/infiniband/hw/ehca/hipz_hw.h @@ -0,0 +1,390 @@ +/* + * IBM eServer eHCA Infiniband device driver for Linux on POWER + * + * eHCA register definitions + * + * Authors: Waleri Fomin + * Christoph Raisch + * Reinhard Ernst + * + * Copyright (c) 2005 IBM Corporation + * + * All rights reserved. + * + * This source code is distributed under a dual license of GPL v2.0 and OpenIB + * BSD. + * + * OpenIB BSD License + * + * 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. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" + * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE + * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE + * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR + * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF + * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR + * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER + * IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + */ + +#ifndef __HIPZ_HW_H__ +#define __HIPZ_HW_H__ + +#include "ehca_tools.h" + +/* QP Table Entry Memory Map */ +struct hipz_qptemm { + u64 qpx_hcr; + u64 qpx_c; + u64 qpx_herr; + u64 qpx_aer; +/* 0x20*/ + u64 qpx_sqa; + u64 qpx_sqc; + u64 qpx_rqa; + u64 qpx_rqc; +/* 0x40*/ + u64 qpx_st; + u64 qpx_pmstate; + u64 qpx_pmfa; + u64 qpx_pkey; +/* 0x60*/ + u64 qpx_pkeya; + u64 qpx_pkeyb; + u64 qpx_pkeyc; + u64 qpx_pkeyd; +/* 0x80*/ + u64 qpx_qkey; + u64 qpx_dqp; + u64 qpx_dlidp; + u64 qpx_portp; +/* 0xa0*/ + u64 qpx_slidp; + u64 qpx_slidpp; + u64 qpx_dlida; + u64 qpx_porta; +/* 0xc0*/ + u64 qpx_slida; + u64 qpx_slidpa; + u64 qpx_slvl; + u64 qpx_ipd; +/* 0xe0*/ + u64 qpx_mtu; + u64 qpx_lato; + u64 qpx_rlimit; + u64 qpx_rnrlimit; +/* 0x100*/ + u64 qpx_t; + u64 qpx_sqhp; + u64 qpx_sqptp; + u64 qpx_nspsn; +/* 0x120*/ + u64 qpx_nspsnhwm; + u64 reserved1; + u64 qpx_sdsi; + u64 qpx_sdsbc; +/* 0x140*/ + u64 qpx_sqwsize; + u64 qpx_sqwts; + u64 qpx_lsn; + u64 qpx_nssn; +/* 0x160 */ + u64 qpx_mor; + u64 qpx_cor; + u64 qpx_sqsize; + u64 qpx_erc; +/* 0x180*/ + u64 qpx_rnrrc; + u64 qpx_ernrwt; + u64 qpx_rnrresp; + u64 qpx_lmsna; +/* 0x1a0 */ + u64 qpx_sqhpc; + u64 qpx_sqcptp; + u64 qpx_sigt; + u64 qpx_wqecnt; +/* 0x1c0*/ + u64 qpx_rqhp; + u64 qpx_rqptp; + u64 qpx_rqsize; + u64 qpx_nrr; +/* 0x1e0*/ + u64 qpx_rdmac; + u64 qpx_nrpsn; + u64 qpx_lapsn; + u64 qpx_lcr; +/* 0x200*/ + u64 qpx_rwc; + u64 qpx_rwva; + u64 qpx_rdsi; + u64 qpx_rdsbc; +/* 0x220*/ + u64 qpx_rqwsize; + u64 qpx_crmsn; + u64 qpx_rdd; + u64 qpx_larpsn; +/* 0x240*/ + u64 qpx_pd; + u64 qpx_scqn; + u64 qpx_rcqn; + u64 qpx_aeqn; +/* 0x260*/ + u64 qpx_aaelog; + u64 qpx_ram; + u64 qpx_rdmaqe0; + u64 qpx_rdmaqe1; +/* 0x280*/ + u64 qpx_rdmaqe2; + u64 qpx_rdmaqe3; + u64 qpx_nrpsnhwm; +/* 0x298*/ + u64 reserved[(0x400 - 0x298) / 8]; +/* 0x400 extended data */ + u64 reserved_ext[(0x500 - 0x400) / 8]; +/* 0x500 */ + u64 reserved2[(0x1000 - 0x500) / 8]; +/* 0x1000 */ +}; + +#define QPX_SQADDER EHCA_BMASK_IBM(48,63) +#define QPX_RQADDER EHCA_BMASK_IBM(48,63) + +#define QPTEMM_OFFSET(x) offsetof(struct hipz_qptemm,x) + +/* MRMWPT Entry Memory Map */ +struct hipz_mrmwmm { + /* 0x00 */ + u64 mrx_hcr; + + u64 mrx_c; + u64 mrx_herr; + u64 mrx_aer; + /* 0x20 */ + u64 mrx_pp; + u64 reserved1; + u64 reserved2; + u64 reserved3; + /* 0x40 */ + u64 reserved4[(0x200 - 0x40) / 8]; + /* 0x200 */ + u64 mrx_ctl[64]; + +}; + +#define MRX_HCR_LPARID_VALID EHCA_BMASK_IBM(0,0) + +#define MRMWMM_OFFSET(x) offsetof(struct hipz_mrmwmm,x) + +struct hipz_qpedmm { + /* 0x00 */ + u64 reserved0[(0x400) / 8]; + /* 0x400 */ + u64 qpedx_phh; + u64 qpedx_ppsgp; + /* 0x410 */ + u64 qpedx_ppsgu; + u64 qpedx_ppdgp; + /* 0x420 */ + u64 qpedx_ppdgu; + u64 qpedx_aph; + /* 0x430 */ + u64 qpedx_apsgp; + u64 qpedx_apsgu; + /* 0x440 */ + u64 qpedx_apdgp; + u64 qpedx_apdgu; + /* 0x450 */ + u64 qpedx_apav; + u64 qpedx_apsav; + /* 0x460 */ + u64 qpedx_hcr; + u64 reserved1[4]; + /* 0x488 */ + u64 qpedx_rrl0; + /* 0x490 */ + u64 qpedx_rrrkey0; + u64 qpedx_rrva0; + /* 0x4a0 */ + u64 reserved2; + u64 qpedx_rrl1; + /* 0x4b0 */ + u64 qpedx_rrrkey1; + u64 qpedx_rrva1; + /* 0x4c0 */ + u64 reserved3; + u64 qpedx_rrl2; + /* 0x4d0 */ + u64 qpedx_rrrkey2; + u64 qpedx_rrva2; + /* 0x4e0 */ + u64 reserved4; + u64 qpedx_rrl3; + /* 0x4f0 */ + u64 qpedx_rrrkey3; + u64 qpedx_rrva3; +}; + +#define QPEDMM_OFFSET(x) offsetof(struct hipz_qpedmm,x) + +/* CQ Table Entry Memory Map */ +struct hipz_cqtemm { + u64 cqx_hcr; + u64 cqx_c; + u64 cqx_herr; + u64 cqx_aer; +/* 0x20 */ + u64 cqx_ptp; + u64 cqx_tp; + u64 cqx_fec; + u64 cqx_feca; +/* 0x40 */ + u64 cqx_ep; + u64 cqx_eq; +/* 0x50 */ + u64 reserved1; + u64 cqx_n0; +/* 0x60 */ + u64 cqx_n1; + u64 reserved2[(0x1000 - 0x60) / 8]; +/* 0x1000 */ +}; + +#define CQX_FEC_CQE_CNT EHCA_BMASK_IBM(32,63) +#define CQX_FECADDER EHCA_BMASK_IBM(32,63) +#define CQX_N0_GENERATE_SOLICITED_COMP_EVENT EHCA_BMASK_IBM(0,0) +#define CQX_N1_GENERATE_COMP_EVENT EHCA_BMASK_IBM(0,0) + +#define CQTEMM_OFFSET(x) offsetof(struct hipz_cqtemm,x) + +/* EQ Table Entry Memory Map */ +struct hipz_eqtemm { + u64 eqx_hcr; + u64 eqx_c; + + u64 eqx_herr; + u64 eqx_aer; +/* 0x20 */ + u64 eqx_ptp; + u64 eqx_tp; + u64 eqx_ssba; + u64 eqx_psba; + +/* 0x40 */ + u64 eqx_cec; + u64 eqx_meql; + u64 eqx_xisbi; + u64 eqx_xisc; +/* 0x60 */ + u64 eqx_it; + +}; + +#define EQTEMM_OFFSET(x) offsetof(struct hipz_eqtemm,x) + +/* access control defines for MR/MW */ +#define HIPZ_ACCESSCTRL_L_WRITE 0x00800000 +#define HIPZ_ACCESSCTRL_R_WRITE 0x00400000 +#define HIPZ_ACCESSCTRL_R_READ 0x00200000 +#define HIPZ_ACCESSCTRL_R_ATOMIC 0x00100000 +#define HIPZ_ACCESSCTRL_MW_BIND 0x00080000 + +/* query hca response block */ +struct hipz_query_hca { + u32 cur_reliable_dg; + u32 cur_qp; + u32 cur_cq; + u32 cur_eq; + u32 cur_mr; + u32 cur_mw; + u32 cur_ee_context; + u32 cur_mcast_grp; + u32 cur_qp_attached_mcast_grp; + u32 reserved1; + u32 cur_ipv6_qp; + u32 cur_eth_qp; + u32 cur_hp_mr; + u32 reserved2[3]; + u32 max_rd_domain; + u32 max_qp; + u32 max_cq; + u32 max_eq; + u32 max_mr; + u32 max_hp_mr; + u32 max_mw; + u32 max_mrwpte; + u32 max_special_mrwpte; + u32 max_rd_ee_context; + u32 max_mcast_grp; + u32 max_total_mcast_qp_attach; + u32 max_mcast_qp_attach; + u32 max_raw_ipv6_qp; + u32 max_raw_ethy_qp; + u32 internal_clock_frequency; + u32 max_pd; + u32 max_ah; + u32 max_cqe; + u32 max_wqes_wq; + u32 max_partitions; + u32 max_rr_ee_context; + u32 max_rr_qp; + u32 max_rr_hca; + u32 max_act_wqs_ee_context; + u32 max_act_wqs_qp; + u32 max_sge; + u32 max_sge_rd; + u32 memory_page_size_supported; + u64 max_mr_size; + u32 local_ca_ack_delay; + u32 num_ports; + u32 vendor_id; + u32 vendor_part_id; + u32 hw_ver; + u64 node_guid; + u64 hca_cap_indicators; + u32 data_counter_register_size; + u32 max_shared_rq; + u32 max_isns_eq; + u32 max_neq; +} __attribute__ ((packed)); + +/* query port response block */ +struct hipz_query_port { + u32 state; + u32 bad_pkey_cntr; + u32 lmc; + u32 lid; + u32 subnet_timeout; + u32 qkey_viol_cntr; + u32 sm_sl; + u32 sm_lid; + u32 capability_mask; + u32 init_type_reply; + u32 pkey_tbl_len; + u32 gid_tbl_len; + u64 gid_prefix; + u32 port_nr; + u16 pkey_entries[16]; + u8 reserved1[32]; + u32 trent_size; + u32 trbuf_size; + u64 max_msg_sz; + u32 max_mtu; + u32 vl_cap; + u8 reserved2[1900]; + u64 guid_entries[255]; +} __attribute__ ((packed)); + +#endif -- 1.4.1 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/