[SeaBIOS] [PATCH v2] nvme: Use the Maximum Queue Entries Supported (MQES) to initialize I/O queues

[Filippo Sironi]

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 at amazon.de>
---
 src/hw/nvme.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/hw/nvme.c b/src/hw/nvme.c
index 946487f4fd43..19a4e7a48d3c 100644
--- a/src/hw/nvme.c
+++ b/src/hw/nvme.c
@@ -20,6 +20,8 @@
 #include "nvme.h"
 #include "nvme-int.h"
 
+#define min(a, b) ({ typeof(a) _a = a; typeof(b) _b = b; _a < _b ? _a : _b; })
+
 static void *
 zalloc_page_aligned(struct zone_s *zone, u32 size)
 {
@@ -318,8 +320,10 @@ nvme_create_io_cq(struct nvme_ctrl *ctrl, struct nvme_cq *cq, u16 q_idx)
 {
     int rc;
     struct nvme_sqe *cmd_create_cq;
+    u16 length;
 
-    rc = nvme_init_cq(ctrl, cq, q_idx, NVME_PAGE_SIZE / sizeof(struct nvme_cqe));
+    length = min(1 + (ctrl->reg->cap & 0xffff), NVME_PAGE_SIZE / sizeof(struct nvme_cqe));
+    rc = nvme_init_cq(ctrl, cq, q_idx, length);
     if (rc) {
         goto err;
     }
@@ -359,8 +363,10 @@ nvme_create_io_sq(struct nvme_ctrl *ctrl, struct nvme_sq *sq, u16 q_idx, struct
 {
     int rc;
     struct nvme_sqe *cmd_create_sq;
+    u16 length;
 
-    rc = nvme_init_sq(ctrl, sq, q_idx, NVME_PAGE_SIZE / sizeof(struct nvme_cqe), cq);
+    length = min(1 + (ctrl->reg->cap & 0xffff), NVME_PAGE_SIZE / sizeof(struct nvme_cqe));
+    rc = nvme_init_sq(ctrl, sq, q_idx, length, cq);
     if (rc) {
         goto err;
     }
-- 
2.7.4