DPDK patches and discussions
 help / color / mirror / Atom feed
From: Raja Zidane <rzidane@nvidia.com>
To: <dev@dpdk.org>
Cc: Matan Azrad <matan@nvidia.com>, <stable@dpdk.org>
Subject: [dpdk-dev] [PATCH V2 3/4] crypto/mlx5: fix the queue size configuration
Date: Mon, 8 Nov 2021 13:09:20 +0000	[thread overview]
Message-ID: <20211108130921.19143-4-rzidane@nvidia.com> (raw)
In-Reply-To: <20211108130921.19143-1-rzidane@nvidia.com>

The DevX interface for QP creation expects the number of WQEBBs.
Wrongly, the number of descriptors was provided to the QP creation.
In addition, the QP size must be a power of 2 what was not guaranteed.
Provide the number of WQEBBs to the QP creation API.
Round up the SQ size to a power of 2.
Rename (sq/rq)_size to num_of_(send/receive)_wqes.

Fixes: 6152534e211e ("crypto/mlx5: support queue pairs operations")
Cc: stable@dpdk.org

Signed-off-by: Raja Zidane <rzidane@nvidia.com>
Acked-by: Matan Azrad <matan@nvidia.com>
---
 drivers/common/mlx5/mlx5_devx_cmds.c    |  14 +--
 drivers/common/mlx5/mlx5_devx_cmds.h    |   5 +-
 drivers/compress/mlx5/mlx5_compress.c   |   4 +-
 drivers/crypto/mlx5/mlx5_crypto.c       | 120 +++++++++++++++++++-----
 drivers/crypto/mlx5/mlx5_crypto.h       |   7 ++
 drivers/regex/mlx5/mlx5_regex_control.c |   4 +-
 drivers/vdpa/mlx5/mlx5_vdpa_event.c     |   4 +-
 7 files changed, 120 insertions(+), 38 deletions(-)

diff --git a/drivers/common/mlx5/mlx5_devx_cmds.c b/drivers/common/mlx5/mlx5_devx_cmds.c
index cecbf541f6..e52b995ee3 100644
--- a/drivers/common/mlx5/mlx5_devx_cmds.c
+++ b/drivers/common/mlx5/mlx5_devx_cmds.c
@@ -832,6 +832,7 @@ mlx5_devx_cmd_query_hca_attr(void *ctx,
 			MLX5_HCA_CAP_OPMOD_GET_CUR);
 	if (!hcattr)
 		return rc;
+	attr->max_wqe_sz_sq = MLX5_GET(cmd_hca_cap, hcattr, max_wqe_sz_sq);
 	attr->flow_counter_bulk_alloc_bitmap =
 			MLX5_GET(cmd_hca_cap, hcattr, flow_counter_bulk_alloc);
 	attr->flow_counters_dump = MLX5_GET(cmd_hca_cap, hcattr,
@@ -2153,21 +2154,22 @@ mlx5_devx_cmd_create_qp(void *ctx,
 		if (attr->log_page_size > MLX5_ADAPTER_PAGE_SHIFT)
 			MLX5_SET(qpc, qpc, log_page_size,
 				 attr->log_page_size - MLX5_ADAPTER_PAGE_SHIFT);
-		if (attr->sq_size) {
-			MLX5_ASSERT(RTE_IS_POWER_OF_2(attr->sq_size));
+		if (attr->num_of_send_wqbbs) {
+			MLX5_ASSERT(RTE_IS_POWER_OF_2(attr->num_of_send_wqbbs));
 			MLX5_SET(qpc, qpc, cqn_snd, attr->cqn);
 			MLX5_SET(qpc, qpc, log_sq_size,
-				 rte_log2_u32(attr->sq_size));
+				 rte_log2_u32(attr->num_of_send_wqbbs));
 		} else {
 			MLX5_SET(qpc, qpc, no_sq, 1);
 		}
-		if (attr->rq_size) {
-			MLX5_ASSERT(RTE_IS_POWER_OF_2(attr->rq_size));
+		if (attr->num_of_receive_wqes) {
+			MLX5_ASSERT(RTE_IS_POWER_OF_2(
+					attr->num_of_receive_wqes));
 			MLX5_SET(qpc, qpc, cqn_rcv, attr->cqn);
 			MLX5_SET(qpc, qpc, log_rq_stride, attr->log_rq_stride -
 				 MLX5_LOG_RQ_STRIDE_SHIFT);
 			MLX5_SET(qpc, qpc, log_rq_size,
-				 rte_log2_u32(attr->rq_size));
+				 rte_log2_u32(attr->num_of_receive_wqes));
 			MLX5_SET(qpc, qpc, rq_type, MLX5_NON_ZERO_RQ);
 		} else {
 			MLX5_SET(qpc, qpc, rq_type, MLX5_ZERO_LEN_RQ);
diff --git a/drivers/common/mlx5/mlx5_devx_cmds.h b/drivers/common/mlx5/mlx5_devx_cmds.h
index 447f76f1f9..d7f71646a3 100644
--- a/drivers/common/mlx5/mlx5_devx_cmds.h
+++ b/drivers/common/mlx5/mlx5_devx_cmds.h
@@ -251,6 +251,7 @@ struct mlx5_hca_attr {
 	uint32_t log_max_mmo_decompress:5;
 	uint32_t umr_modify_entity_size_disabled:1;
 	uint32_t umr_indirect_mkey_disabled:1;
+	uint16_t max_wqe_sz_sq;
 };
 
 /* LAG Context. */
@@ -477,9 +478,9 @@ struct mlx5_devx_qp_attr {
 	uint32_t uar_index:24;
 	uint32_t cqn:24;
 	uint32_t log_page_size:5;
-	uint32_t rq_size:17; /* Must be power of 2. */
+	uint32_t num_of_receive_wqes:17; /* Must be power of 2. */
 	uint32_t log_rq_stride:3;
-	uint32_t sq_size:17; /* Must be power of 2. */
+	uint32_t num_of_send_wqbbs:17; /* Must be power of 2. */
 	uint32_t ts_format:2;
 	uint32_t dbr_umem_valid:1;
 	uint32_t dbr_umem_id;
diff --git a/drivers/compress/mlx5/mlx5_compress.c b/drivers/compress/mlx5/mlx5_compress.c
index d5511aebdf..7813af38e6 100644
--- a/drivers/compress/mlx5/mlx5_compress.c
+++ b/drivers/compress/mlx5/mlx5_compress.c
@@ -244,8 +244,8 @@ mlx5_compress_qp_setup(struct rte_compressdev *dev, uint16_t qp_id,
 	qp_attr.cqn = qp->cq.cq->id;
 	qp_attr.ts_format =
 		mlx5_ts_format_conv(priv->cdev->config.hca_attr.qp_ts_format);
-	qp_attr.rq_size = 0;
-	qp_attr.sq_size = RTE_BIT32(log_ops_n);
+	qp_attr.num_of_receive_wqes = 0;
+	qp_attr.num_of_send_wqbbs = RTE_BIT32(log_ops_n);
 	qp_attr.mmo = priv->mmo_decomp_qp && priv->mmo_comp_qp
 			&& priv->mmo_dma_qp;
 	ret = mlx5_devx_qp_create(priv->cdev->ctx, &qp->qp, log_ops_n, &qp_attr,
diff --git a/drivers/crypto/mlx5/mlx5_crypto.c b/drivers/crypto/mlx5/mlx5_crypto.c
index 1d0f1f3cfc..9fdbee9be1 100644
--- a/drivers/crypto/mlx5/mlx5_crypto.c
+++ b/drivers/crypto/mlx5/mlx5_crypto.c
@@ -545,7 +545,7 @@ mlx5_crypto_qp_init(struct mlx5_crypto_priv *priv, struct mlx5_crypto_qp *qp)
 		ucseg->if_cf_toe_cq_res = RTE_BE32(1u << MLX5_UMRC_IF_OFFSET);
 		ucseg->mkey_mask = RTE_BE64(1u << 0); /* Mkey length bit. */
 		ucseg->ko_to_bs = rte_cpu_to_be_32
-			((RTE_ALIGN(priv->max_segs_num, 4u) <<
+			((MLX5_CRYPTO_KLM_SEGS_NUM(priv->umr_wqe_size) <<
 			 MLX5_UMRC_KO_OFFSET) | (4 << MLX5_UMRC_TO_BS_OFFSET));
 		bsf->keytag = priv->keytag;
 		/* Init RDMA WRITE WQE. */
@@ -569,7 +569,7 @@ mlx5_crypto_indirect_mkeys_prepare(struct mlx5_crypto_priv *priv,
 		.umr_en = 1,
 		.crypto_en = 1,
 		.set_remote_rw = 1,
-		.klm_num = RTE_ALIGN(priv->max_segs_num, 4),
+		.klm_num = MLX5_CRYPTO_KLM_SEGS_NUM(priv->umr_wqe_size),
 	};
 
 	for (umr = (struct mlx5_umr_wqe *)qp->qp_obj.umem_buf, i = 0;
@@ -597,6 +597,7 @@ mlx5_crypto_queue_pair_setup(struct rte_cryptodev *dev, uint16_t qp_id,
 	uint16_t log_nb_desc = rte_log2_u32(qp_conf->nb_descriptors);
 	uint32_t ret;
 	uint32_t alloc_size = sizeof(*qp);
+	uint32_t log_wqbb_n;
 	struct mlx5_devx_cq_attr cq_attr = {
 		.uar_page_id = mlx5_os_get_devx_uar_page_id(priv->uar.obj),
 	};
@@ -619,14 +620,16 @@ mlx5_crypto_queue_pair_setup(struct rte_cryptodev *dev, uint16_t qp_id,
 		DRV_LOG(ERR, "Failed to create CQ.");
 		goto error;
 	}
+	log_wqbb_n = rte_log2_u32(RTE_BIT32(log_nb_desc) *
+				(priv->wqe_set_size / MLX5_SEND_WQE_BB));
 	attr.pd = priv->cdev->pdn;
 	attr.uar_index = mlx5_os_get_devx_uar_page_id(priv->uar.obj);
 	attr.cqn = qp->cq_obj.cq->id;
-	attr.rq_size = 0;
-	attr.sq_size = RTE_BIT32(log_nb_desc);
+	attr.num_of_receive_wqes = 0;
+	attr.num_of_send_wqbbs = RTE_BIT32(log_wqbb_n);
 	attr.ts_format =
 		mlx5_ts_format_conv(priv->cdev->config.hca_attr.qp_ts_format);
-	ret = mlx5_devx_qp_create(priv->cdev->ctx, &qp->qp_obj, log_nb_desc,
+	ret = mlx5_devx_qp_create(priv->cdev->ctx, &qp->qp_obj, log_wqbb_n,
 				  &attr, socket_id);
 	if (ret) {
 		DRV_LOG(ERR, "Failed to create QP.");
@@ -747,10 +750,8 @@ mlx5_crypto_args_check_handler(const char *key, const char *val, void *opaque)
 		return -errno;
 	}
 	if (strcmp(key, "max_segs_num") == 0) {
-		if (!tmp || tmp > MLX5_CRYPTO_MAX_SEGS) {
-			DRV_LOG(WARNING, "Invalid max_segs_num: %d, should"
-				" be less than %d.",
-				(uint32_t)tmp, MLX5_CRYPTO_MAX_SEGS);
+		if (!tmp) {
+			DRV_LOG(ERR, "max_segs_num must be greater than 0.");
 			rte_errno = EINVAL;
 			return -rte_errno;
 		}
@@ -809,6 +810,81 @@ mlx5_crypto_parse_devargs(struct rte_devargs *devargs,
 	return 0;
 }
 
+/*
+ * Calculate UMR WQE size and RDMA Write WQE size with the
+ * following limitations:
+ *	- Each WQE size is multiple of 64.
+ *	- The summarize of both UMR WQE and RDMA_W WQE is a power of 2.
+ *	- The number of entries in the UMR WQE's KLM list is multiple of 4.
+ */
+static void
+mlx5_crypto_get_wqe_sizes(uint32_t segs_num, uint32_t *umr_size,
+			uint32_t *rdmaw_size)
+{
+	uint32_t diff, wqe_set_size;
+
+	*umr_size = MLX5_CRYPTO_UMR_WQE_STATIC_SIZE +
+			RTE_ALIGN(segs_num, 4) *
+			sizeof(struct mlx5_wqe_dseg);
+	/* Make sure UMR WQE size is multiple of WQBB. */
+	*umr_size = RTE_ALIGN(*umr_size, MLX5_SEND_WQE_BB);
+	*rdmaw_size = sizeof(struct mlx5_rdma_write_wqe) +
+			sizeof(struct mlx5_wqe_dseg) *
+			(segs_num <= 2 ? 2 : 2 +
+			RTE_ALIGN(segs_num - 2, 4));
+	/* Make sure RDMA_WRITE WQE size is multiple of WQBB. */
+	*rdmaw_size = RTE_ALIGN(*rdmaw_size, MLX5_SEND_WQE_BB);
+	wqe_set_size = *rdmaw_size + *umr_size;
+	diff = rte_align32pow2(wqe_set_size) - wqe_set_size;
+	/* Make sure wqe_set size is power of 2. */
+	if (diff)
+		*umr_size += diff;
+}
+
+static uint8_t
+mlx5_crypto_max_segs_num(uint16_t max_wqe_size)
+{
+	int klms_sizes = max_wqe_size - MLX5_CRYPTO_UMR_WQE_STATIC_SIZE;
+	uint32_t max_segs_cap = RTE_ALIGN_FLOOR(klms_sizes, MLX5_SEND_WQE_BB) /
+			sizeof(struct mlx5_wqe_dseg);
+
+	MLX5_ASSERT(klms_sizes >= MLX5_SEND_WQE_BB);
+	while (max_segs_cap) {
+		uint32_t umr_wqe_size, rdmw_wqe_size;
+
+		mlx5_crypto_get_wqe_sizes(max_segs_cap, &umr_wqe_size,
+						&rdmw_wqe_size);
+		if (umr_wqe_size <= max_wqe_size &&
+				rdmw_wqe_size <= max_wqe_size)
+			break;
+		max_segs_cap -= 4;
+	}
+	return max_segs_cap;
+}
+
+static int
+mlx5_crypto_configure_wqe_size(struct mlx5_crypto_priv *priv,
+				uint16_t max_wqe_size, uint32_t max_segs_num)
+{
+	uint32_t rdmw_wqe_size, umr_wqe_size;
+
+	mlx5_crypto_get_wqe_sizes(max_segs_num, &umr_wqe_size,
+					&rdmw_wqe_size);
+	priv->wqe_set_size = rdmw_wqe_size + umr_wqe_size;
+	if (umr_wqe_size > max_wqe_size ||
+				rdmw_wqe_size > max_wqe_size) {
+		DRV_LOG(ERR, "Invalid max_segs_num: %u. should be %u or lower.",
+			max_segs_num,
+			mlx5_crypto_max_segs_num(max_wqe_size));
+		rte_errno = EINVAL;
+		return -EINVAL;
+	}
+	priv->umr_wqe_size = (uint16_t)umr_wqe_size;
+	priv->umr_wqe_stride = priv->umr_wqe_size / MLX5_SEND_WQE_BB;
+	priv->max_rdmar_ds = rdmw_wqe_size / sizeof(struct mlx5_wqe_dseg);
+	return 0;
+}
+
 static int
 mlx5_crypto_dev_probe(struct mlx5_common_device *cdev)
 {
@@ -824,7 +900,6 @@ mlx5_crypto_dev_probe(struct mlx5_common_device *cdev)
 				RTE_CRYPTODEV_PMD_DEFAULT_MAX_NB_QUEUE_PAIRS,
 	};
 	const char *ibdev_name = mlx5_os_get_ctx_device_name(cdev->ctx);
-	uint16_t rdmw_wqe_size;
 	int ret;
 
 	if (rte_eal_process_type() != RTE_PROC_PRIMARY) {
@@ -873,20 +948,17 @@ mlx5_crypto_dev_probe(struct mlx5_common_device *cdev)
 	}
 	priv->login_obj = login;
 	priv->keytag = rte_cpu_to_be_64(devarg_prms.keytag);
-	priv->max_segs_num = devarg_prms.max_segs_num;
-	priv->umr_wqe_size = sizeof(struct mlx5_wqe_umr_bsf_seg) +
-			     sizeof(struct mlx5_wqe_cseg) +
-			     sizeof(struct mlx5_wqe_umr_cseg) +
-			     sizeof(struct mlx5_wqe_mkey_cseg) +
-			     RTE_ALIGN(priv->max_segs_num, 4) *
-			     sizeof(struct mlx5_wqe_dseg);
-	rdmw_wqe_size = sizeof(struct mlx5_rdma_write_wqe) +
-			      sizeof(struct mlx5_wqe_dseg) *
-			      (priv->max_segs_num <= 2 ? 2 : 2 +
-			       RTE_ALIGN(priv->max_segs_num - 2, 4));
-	priv->wqe_set_size = priv->umr_wqe_size + rdmw_wqe_size;
-	priv->umr_wqe_stride = priv->umr_wqe_size / MLX5_SEND_WQE_BB;
-	priv->max_rdmar_ds = rdmw_wqe_size / sizeof(struct mlx5_wqe_dseg);
+	ret = mlx5_crypto_configure_wqe_size(priv,
+		cdev->config.hca_attr.max_wqe_sz_sq, devarg_prms.max_segs_num);
+	if (ret) {
+		mlx5_devx_uar_release(&priv->uar);
+		rte_cryptodev_pmd_destroy(priv->crypto_dev);
+		return -1;
+	}
+	DRV_LOG(INFO, "Max number of segments: %u.",
+		(unsigned int)RTE_MIN(
+			MLX5_CRYPTO_KLM_SEGS_NUM(priv->umr_wqe_size),
+			(uint16_t)(priv->max_rdmar_ds - 2)));
 	pthread_mutex_lock(&priv_list_lock);
 	TAILQ_INSERT_TAIL(&mlx5_crypto_priv_list, priv, next);
 	pthread_mutex_unlock(&priv_list_lock);
diff --git a/drivers/crypto/mlx5/mlx5_crypto.h b/drivers/crypto/mlx5/mlx5_crypto.h
index 135cd78212..f04b3d8c20 100644
--- a/drivers/crypto/mlx5/mlx5_crypto.h
+++ b/drivers/crypto/mlx5/mlx5_crypto.h
@@ -16,6 +16,13 @@
 
 #define MLX5_CRYPTO_DEK_HTABLE_SZ (1 << 11)
 #define MLX5_CRYPTO_KEY_LENGTH 80
+#define MLX5_CRYPTO_UMR_WQE_STATIC_SIZE (sizeof(struct mlx5_wqe_cseg) +\
+					sizeof(struct mlx5_wqe_umr_cseg) +\
+					sizeof(struct mlx5_wqe_mkey_cseg) +\
+					sizeof(struct mlx5_wqe_umr_bsf_seg))
+#define MLX5_CRYPTO_KLM_SEGS_NUM(umr_wqe_sz) ((umr_wqe_sz -\
+					MLX5_CRYPTO_UMR_WQE_STATIC_SIZE) /\
+					MLX5_WSEG_SIZE)
 
 struct mlx5_crypto_priv {
 	TAILQ_ENTRY(mlx5_crypto_priv) next;
diff --git a/drivers/regex/mlx5/mlx5_regex_control.c b/drivers/regex/mlx5/mlx5_regex_control.c
index d184b1a921..46e400a93f 100644
--- a/drivers/regex/mlx5/mlx5_regex_control.c
+++ b/drivers/regex/mlx5/mlx5_regex_control.c
@@ -149,8 +149,8 @@ regex_ctrl_create_hw_qp(struct mlx5_regex_priv *priv, struct mlx5_regex_qp *qp,
 	qp_obj->qpn = q_ind;
 	qp_obj->ci = 0;
 	qp_obj->pi = 0;
-	attr.rq_size = 0;
-	attr.sq_size = RTE_BIT32(MLX5_REGEX_WQE_LOG_NUM(priv->has_umr,
+	attr.num_of_receive_wqes = 0;
+	attr.num_of_send_wqbbs = RTE_BIT32(MLX5_REGEX_WQE_LOG_NUM(priv->has_umr,
 			log_nb_desc));
 	attr.mmo = priv->mmo_regex_qp_cap;
 	ret = mlx5_devx_qp_create(priv->cdev->ctx, &qp_obj->qp_obj,
diff --git a/drivers/vdpa/mlx5/mlx5_vdpa_event.c b/drivers/vdpa/mlx5/mlx5_vdpa_event.c
index 9cc71714a2..657c39dae1 100644
--- a/drivers/vdpa/mlx5/mlx5_vdpa_event.c
+++ b/drivers/vdpa/mlx5/mlx5_vdpa_event.c
@@ -589,9 +589,9 @@ mlx5_vdpa_event_qp_create(struct mlx5_vdpa_priv *priv, uint16_t desc_n,
 	}
 	attr.uar_index = mlx5_os_get_devx_uar_page_id(priv->uar.obj);
 	attr.cqn = eqp->cq.cq_obj.cq->id;
-	attr.rq_size = RTE_BIT32(log_desc_n);
+	attr.num_of_receive_wqes = RTE_BIT32(log_desc_n);
 	attr.log_rq_stride = rte_log2_u32(MLX5_WSEG_SIZE);
-	attr.sq_size = 0; /* No need SQ. */
+	attr.num_of_send_wqbbs = 0; /* No need SQ. */
 	attr.ts_format =
 		mlx5_ts_format_conv(priv->cdev->config.hca_attr.qp_ts_format);
 	ret = mlx5_devx_qp_create(priv->cdev->ctx, &(eqp->sw_qp), log_desc_n,
-- 
2.17.1


  parent reply	other threads:[~2021-11-08 13:10 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-04 12:49 [dpdk-dev] [PATCH 0/4] fixes to queue size config Raja Zidane
2021-11-04 12:49 ` [dpdk-dev] [PATCH 1/4] common/mlx5: fix overflows in DevX queues size calculations Raja Zidane
2021-11-04 12:49 ` [dpdk-dev] [PATCH 2/4] crypto/mlx5: fix driver destroy before the configuration Raja Zidane
2021-11-04 12:49 ` [dpdk-dev] [PATCH 3/4] crypto/mlx5: fix the queue size configuration Raja Zidane
2021-11-04 18:59   ` Tal Shnaiderman
2021-11-04 12:49 ` [dpdk-dev] [PATCH 4/4] common/mlx5: fix RQ size configuration in QP create Raja Zidane
2021-11-08  9:02 ` [dpdk-dev] [PATCH 0/4] fixes to queue size config Thomas Monjalon
2021-11-08 12:33 ` [dpdk-dev] [PATCH V2 " Raja Zidane
2021-11-08 12:33   ` [dpdk-dev] [PATCH V2 1/4] common/mlx5: fix overflows in DevX queues size calculations Raja Zidane
2021-11-08 12:33   ` [dpdk-dev] [PATCH V2 2/4] crypto/mlx5: fix driver destroy before the configuration Raja Zidane
2021-11-08 12:33   ` [dpdk-dev] [PATCH V2 3/4] crypto/mlx5: fix the queue size configuration Raja Zidane
2021-11-08 12:33   ` [dpdk-dev] [PATCH V2 4/4] common/mlx5: fix RQ size configuration in QP create Raja Zidane
2021-11-08 13:09   ` [dpdk-dev] [PATCH V2 0/4] fixes to queue size config Raja Zidane
2021-11-08 13:09     ` [dpdk-dev] [PATCH V2 1/4] common/mlx5: fix overflows in DevX queues size calculations Raja Zidane
2021-11-08 13:09     ` [dpdk-dev] [PATCH V2 2/4] crypto/mlx5: fix driver destroy before the configuration Raja Zidane
2021-11-08 13:09     ` Raja Zidane [this message]
2021-11-08 13:09     ` [dpdk-dev] [PATCH V2 4/4] common/mlx5: fix RQ size configuration in QP create Raja Zidane
2021-11-08 18:44     ` [dpdk-dev] [PATCH V2 0/4] fixes to queue size config Thomas Monjalon

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20211108130921.19143-4-rzidane@nvidia.com \
    --to=rzidane@nvidia.com \
    --cc=dev@dpdk.org \
    --cc=matan@nvidia.com \
    --cc=stable@dpdk.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).