[RFC 4/4] nvme: add bit bucket support

[Keith Busch]

From: Keith Busch <kbusch at kernel.org>

Set the queue for bit bucket support if the hardware and driver support
it. The nvme pci driver will recognize the special bitbucket page for
read commands and set up an appropriate sg descriptor for it.

Signed-off-by: Keith Busch <kbusch at kernel.org>
---
 drivers/nvme/host/core.c |  3 +++
 drivers/nvme/host/nvme.h |  6 ++++++
 drivers/nvme/host/pci.c  | 17 +++++++++++++++--
 include/linux/nvme.h     |  2 ++
 4 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index e1846d04817f..bea054565eed 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3928,6 +3928,9 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid,
 	if (ctrl->ops->flags & NVME_F_PCI_P2PDMA)
 		blk_queue_flag_set(QUEUE_FLAG_PCI_P2PDMA, ns->queue);
 
+	if (nvme_ctrl_sgl_bb_supported(ctrl) && ctrl->ops->flags & NVME_F_BB)
+		blk_queue_flag_set(QUEUE_FLAG_BIT_BUCKET, ns->queue);
+
 	ns->ctrl = ctrl;
 	kref_init(&ns->kref);
 
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index a2b53ca63335..91d75f95fe39 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -495,6 +495,7 @@ struct nvme_ctrl_ops {
 #define NVME_F_FABRICS			(1 << 0)
 #define NVME_F_METADATA_SUPPORTED	(1 << 1)
 #define NVME_F_PCI_P2PDMA		(1 << 2)
+#define NVME_F_BB			(1 << 3)
 	int (*reg_read32)(struct nvme_ctrl *ctrl, u32 off, u32 *val);
 	int (*reg_write32)(struct nvme_ctrl *ctrl, u32 off, u32 val);
 	int (*reg_read64)(struct nvme_ctrl *ctrl, u32 off, u64 *val);
@@ -957,6 +958,11 @@ static inline bool nvme_ctrl_sgl_supported(struct nvme_ctrl *ctrl)
 	return ctrl->sgls & ((1 << 0) | (1 << 1));
 }
 
+static inline bool nvme_ctrl_sgl_bb_supported(struct nvme_ctrl *ctrl)
+{
+	return ctrl->sgls & (1 << 16);
+}
+
 u32 nvme_command_effects(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
 			 u8 opcode);
 int nvme_execute_passthru_rq(struct request *rq);
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 3aacf1c0d5a5..83e057f44867 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -535,6 +535,8 @@ static inline bool nvme_pci_use_sgls(struct nvme_dev *dev, struct request *req)
 
 	avg_seg_size = DIV_ROUND_UP(blk_rq_payload_bytes(req), nseg);
 
+	if (req->rq_flags & RQF_BIT_BUCKET)
+		return true;
 	if (!nvme_ctrl_sgl_supported(&dev->ctrl))
 		return false;
 	if (!iod->nvmeq->qid)
@@ -724,6 +726,13 @@ static void nvme_pci_sgl_set_data(struct nvme_sgl_desc *sge,
 	sge->type = NVME_SGL_FMT_DATA_DESC << 4;
 }
 
+static void nvme_pci_sgl_set_bb(struct nvme_sgl_desc *sge,
+				struct scatterlist *sg)
+{
+	sge->length = cpu_to_le32(sg_dma_len(sg));
+	sge->type = NVME_SGL_FMT_BB_DESC << 4;
+}
+
 static void nvme_pci_sgl_set_seg(struct nvme_sgl_desc *sge,
 		dma_addr_t dma_addr, int entries)
 {
@@ -789,7 +798,10 @@ static blk_status_t nvme_pci_setup_sgls(struct nvme_dev *dev,
 			nvme_pci_sgl_set_seg(link, sgl_dma, entries);
 		}
 
-		nvme_pci_sgl_set_data(&sg_list[i++], sg);
+		if (rq_data_dir(req) == READ && blk_is_bit_bucket(sg_page(sg)))
+			nvme_pci_sgl_set_bb(&sg_list[i++], sg);
+		else
+			nvme_pci_sgl_set_data(&sg_list[i++], sg);
 		sg = sg_next(sg);
 	} while (--entries > 0);
 
@@ -2973,7 +2985,8 @@ static const struct nvme_ctrl_ops nvme_pci_ctrl_ops = {
 	.name			= "pcie",
 	.module			= THIS_MODULE,
 	.flags			= NVME_F_METADATA_SUPPORTED |
-				  NVME_F_PCI_P2PDMA,
+				  NVME_F_PCI_P2PDMA |
+				  NVME_F_BB,
 	.reg_read32		= nvme_pci_reg_read32,
 	.reg_write32		= nvme_pci_reg_write32,
 	.reg_read64		= nvme_pci_reg_read64,
diff --git a/include/linux/nvme.h b/include/linux/nvme.h
index f626a445d1a8..27d568633e6e 100644
--- a/include/linux/nvme.h
+++ b/include/linux/nvme.h
@@ -796,6 +796,7 @@ enum {
  *
  * For struct nvme_sgl_desc:
  *   @NVME_SGL_FMT_DATA_DESC:		data block descriptor
+ *   @NVME_SGL_FMT_BB_DESC:		bit buckect descriptor
  *   @NVME_SGL_FMT_SEG_DESC:		sgl segment descriptor
  *   @NVME_SGL_FMT_LAST_SEG_DESC:	last sgl segment descriptor
  *
@@ -807,6 +808,7 @@ enum {
  */
 enum {
 	NVME_SGL_FMT_DATA_DESC		= 0x00,
+	NVME_SGL_FMT_BB_DESC		= 0x01,
 	NVME_SGL_FMT_SEG_DESC		= 0x02,
 	NVME_SGL_FMT_LAST_SEG_DESC	= 0x03,
 	NVME_KEY_SGL_FMT_DATA_DESC	= 0x04,
-- 
2.30.2