[PATCH] nvme: set controller enable bit in a separate write

[Niklas Cassel]

The NVM Express Base Specification 2.0 specifies in the description
of the CC – Controller Configuration register:
"Host software shall set the Arbitration Mechanism Selected (CC.AMS),
the Memory Page Size (CC.MPS), and the I/O Command Set Selected (CC.CSS)
to valid values prior to enabling the controller by setting CC.EN to ‘1’.

While we haven't seen any controller misbehaving while setting all bits
in a single write, let's do it in the order that it is written in the
spec, as there could potentially be controllers that are implemented to
rely on the configuration bits being set before enabling the controller.

Signed-off-by: Niklas Cassel <niklas.cassel at wdc.com>
---
 drivers/nvme/host/core.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 72f7c955c707..a4b108a720aa 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -2227,6 +2227,16 @@ int nvme_enable_ctrl(struct nvme_ctrl *ctrl)
 	ctrl->ctrl_config |= (NVME_CTRL_PAGE_SHIFT - 12) << NVME_CC_MPS_SHIFT;
 	ctrl->ctrl_config |= NVME_CC_AMS_RR | NVME_CC_SHN_NONE;
 	ctrl->ctrl_config |= NVME_CC_IOSQES | NVME_CC_IOCQES;
+
+	ret = ctrl->ops->reg_write32(ctrl, NVME_REG_CC, ctrl->ctrl_config);
+	if (ret)
+		return ret;
+
+	/* Flush write to device (required if transport is PCI) */
+	ret = ctrl->ops->reg_read32(ctrl, NVME_REG_CC, &ctrl->ctrl_config);
+	if (ret)
+		return ret;
+
 	ctrl->ctrl_config |= NVME_CC_ENABLE;
 
 	ret = ctrl->ops->reg_write32(ctrl, NVME_REG_CC, ctrl->ctrl_config);
-- 
2.36.1