nvme: Use the Maximum Queue Entries Supported (MQES) to initialize I/O queues

Use the Maximum Queue Entries Supported (MQES) to initialize I/O queues
depth rather than picking a fixed number (256) which might not be
supported by some NVMe controllers (the NVMe specification says that an
NVMe controller may support any number between 2 to 4096).

Still cap the I/O queues depth to 256 since, during my testing, SeaBIOS
was running out of memory when using something higher than 256 (4096 on
the NVMe controller that I've had a chance to try).

Signed-off-by: Filippo Sironi <sironi@amazon.de>
diff --git a/src/hw/nvme.c b/src/hw/nvme.c
index 946487f..e6d739d 100644
--- a/src/hw/nvme.c
+++ b/src/hw/nvme.c
@@ -318,8 +318,11 @@
 {
     int rc;
     struct nvme_sqe *cmd_create_cq;
+    u16 length = 1 + (ctrl->reg->cap & 0xffff);
+    if (length > NVME_PAGE_SIZE / sizeof(struct nvme_cqe))
+        length = NVME_PAGE_SIZE / sizeof(struct nvme_cqe);
 
-    rc = nvme_init_cq(ctrl, cq, q_idx, NVME_PAGE_SIZE / sizeof(struct nvme_cqe));
+    rc = nvme_init_cq(ctrl, cq, q_idx, length);
     if (rc) {
         goto err;
     }
@@ -359,8 +362,11 @@
 {
     int rc;
     struct nvme_sqe *cmd_create_sq;
+    u16 length = 1 + (ctrl->reg->cap & 0xffff);
+    if (length > NVME_PAGE_SIZE / sizeof(struct nvme_cqe))
+        length = NVME_PAGE_SIZE / sizeof(struct nvme_cqe);
 
-    rc = nvme_init_sq(ctrl, sq, q_idx, NVME_PAGE_SIZE / sizeof(struct nvme_cqe), cq);
+    rc = nvme_init_sq(ctrl, sq, q_idx, length, cq);
     if (rc) {
         goto err;
     }