nvme-pci: implement the HMB entry number and size limitations

Adds support for the new Host Memory Buffer Minimum Descriptor Entry Size
and Host Memory Maximum Descriptors Entries field that were added in
TP 4002 HMB Enhancements.  These allow the controller to advertise
limits for the usual number of segments in the host memory buffer, as
well as a minimum usable per-segment size.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <keith.busch@intel.com>

drivers/nvme/host/core.c

@@ -1897,6 +1897,8 @@ int nvme_init_identify(struct nvme_ctrl *ctrl)
 		ctrl->cntlid = le16_to_cpu(id->cntlid);
 		ctrl->hmpre = le32_to_cpu(id->hmpre);
 		ctrl->hmmin = le32_to_cpu(id->hmmin);
+		ctrl->hmminds = le32_to_cpu(id->hmminds);
+		ctrl->hmmaxd = le16_to_cpu(id->hmmaxd);
 	}
 
 	kfree(id);

drivers/nvme/host/nvme.h

@@ -181,8 +181,11 @@ struct nvme_ctrl {
 	u64 ps_max_latency_us;
 	bool apst_enabled;
 
+	/* PCIe only: */
 	u32 hmpre;
 	u32 hmmin;
+	u32 hmminds;
+	u16 hmmaxd;
 
 	/* Fabrics only */
 	u16 sqsize;

drivers/nvme/host/pci.c

@@ -1625,6 +1625,10 @@ static int __nvme_alloc_host_mem(struct nvme_dev *dev, u64 preferred,
 	tmp = (preferred + chunk_size - 1);
 	do_div(tmp, chunk_size);
 	max_entries = tmp;
+
+	if (dev->ctrl.hmmaxd && dev->ctrl.hmmaxd < max_entries)
+		max_entries = dev->ctrl.hmmaxd;
+
 	descs = dma_zalloc_coherent(dev->dev, max_entries * sizeof(*descs),
 			&descs_dma, GFP_KERNEL);
 	if (!descs)
@@ -1681,7 +1685,7 @@ static int nvme_alloc_host_mem(struct nvme_dev *dev, u64 min, u64 preferred)
 
 	/* start big and work our way down */
 	for (chunk_size = min_t(u64, preferred, PAGE_SIZE * MAX_ORDER_NR_PAGES);
-	     chunk_size >= PAGE_SIZE * 2;
+	     chunk_size >= max_t(u32, dev->ctrl.hmminds * 4096, PAGE_SIZE * 2);
 	     chunk_size /= 2) {
 		if (!__nvme_alloc_host_mem(dev, preferred, chunk_size)) {
 			if (!min || dev->host_mem_size >= min)

include/linux/nvme.h

@@ -226,7 +226,9 @@ struct nvme_id_ctrl {
 	__le16			mntmt;
 	__le16			mxtmt;
 	__le32			sanicap;
-	__u8			rsvd332[180];
+	__le32			hmminds;
+	__le16			hmmaxd;
+	__u8			rsvd338[174];
 	__u8			sqes;
 	__u8			cqes;
 	__le16			maxcmd;