git: a8ce65544595 - stable/13 - nvme_ctrlr_enable: Remove unnecessary 5ms delays

The branch stable/13 has been updated by mav:

URL: https://cgit.FreeBSD.org/src/commit/?id=a8ce65544595144b81130b7524ac684084d5220e

commit a8ce65544595144b81130b7524ac684084d5220e
Author:     Warner Losh <imp@FreeBSD.org>
AuthorDate: 2021-10-01 16:47:27 +0000
Commit:     Alexander Motin <mav@FreeBSD.org>
CommitDate: 2022-01-21 02:07:30 +0000

    nvme_ctrlr_enable: Remove unnecessary 5ms delays
    
    Remove the 5ms delays after writing the administrative queue
    registers. These delays are from the very earliest days of the driver
    (they are in the first commit) and were most likely vestiges of the
    Chatham NVMe prototype card that was used to create this driver. Many of
    the workarounds necessary for it aren't necessary for standards
    compliant cards. The original driver had other areas marked for Chatham,
    but these were not. They are unneeded. There's three lines of supporting
    evidence.
    
    First, the NVMe standards make no mention of a delay time after these
    registers are written. Second, the Linux driver doesn't have them, even
    as an option. Third, all my nvme cards work w/o them.
    
    To be safe, add a write barrier between setting up the admin queue and
    enabling the controller.
    
    Sponsored by:           Netflix
    Reviewed by:            mav
    Differential Revision:  https://reviews.freebsd.org/D32247
    
    (cherry picked from commit d5fca1dc1d7de15695b65374d6457abd29a747ee)
---
 sys/dev/nvme/nvme_ctrlr.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/sys/dev/nvme/nvme_ctrlr.c b/sys/dev/nvme/nvme_ctrlr.c
index 39cde3f065dd..897d832047ce 100644
--- a/sys/dev/nvme/nvme_ctrlr.c
+++ b/sys/dev/nvme/nvme_ctrlr.c
@@ -52,6 +52,12 @@ __FBSDID("$FreeBSD$");
 static void nvme_ctrlr_construct_and_submit_aer(struct nvme_controller *ctrlr,
 						struct nvme_async_event_request *aer);
 
+static void
+nvme_ctrlr_barrier(struct nvme_controller *ctrlr, int flags)
+{
+	bus_barrier(ctrlr->resource, 0, rman_get_size(ctrlr->resource), flags);
+}
+
 static void
 nvme_ctrlr_devctl_log(struct nvme_controller *ctrlr, const char *type, const char *msg, ...)
 {
@@ -356,9 +362,7 @@ nvme_ctrlr_enable(struct nvme_controller *ctrlr)
 	}
 
 	nvme_mmio_write_8(ctrlr, asq, ctrlr->adminq.cmd_bus_addr);
-	DELAY(5000);
 	nvme_mmio_write_8(ctrlr, acq, ctrlr->adminq.cpl_bus_addr);
-	DELAY(5000);
 
 	/* acqs and asqs are 0-based. */
 	qsize = ctrlr->adminq.num_entries - 1;
@@ -367,7 +371,6 @@ nvme_ctrlr_enable(struct nvme_controller *ctrlr)
 	aqa = (qsize & NVME_AQA_REG_ACQS_MASK) << NVME_AQA_REG_ACQS_SHIFT;
 	aqa |= (qsize & NVME_AQA_REG_ASQS_MASK) << NVME_AQA_REG_ASQS_SHIFT;
 	nvme_mmio_write_4(ctrlr, aqa, aqa);
-	DELAY(5000);
 
 	/* Initialization values for CC */
 	cc = 0;
@@ -381,6 +384,7 @@ nvme_ctrlr_enable(struct nvme_controller *ctrlr)
 	/* This evaluates to 0, which is according to spec. */
 	cc |= (PAGE_SIZE >> 13) << NVME_CC_REG_MPS_SHIFT;
 
+	nvme_ctrlr_barrier(ctrlr, BUS_SPACE_BARRIER_WRITE);
 	nvme_mmio_write_4(ctrlr, cc, cc);
 
 	return (nvme_ctrlr_wait_for_ready(ctrlr, 1));