git: 77054a897f64 - main - nvme: Explain a workaround a little better

[Warner Losh]

The branch main has been updated by imp:

URL: https://cgit.FreeBSD.org/src/commit/?id=77054a897f6440632267e75ebe31793c7555b79e

commit 77054a897f6440632267e75ebe31793c7555b79e
Author:     Warner Losh <imp at FreeBSD.org>
AuthorDate: 2021-10-01 15:53:10 +0000
Commit:     Warner Losh <imp at FreeBSD.org>
CommitDate: 2021-10-01 16:56:10 +0000

    nvme: Explain a workaround a little better
    
    The don't touch the mmio of the drive after we do a EN 1->0 transition
    is only for a tiny number of dirves that have this unforunate issue.
    
    Sponsored by:           Netflix
---
 sys/dev/nvme/nvme_ctrlr.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/sys/dev/nvme/nvme_ctrlr.c b/sys/dev/nvme/nvme_ctrlr.c
index 10b30c584f71..eb95fa33b90b 100644
--- a/sys/dev/nvme/nvme_ctrlr.c
+++ b/sys/dev/nvme/nvme_ctrlr.c
@@ -318,10 +318,10 @@ nvme_ctrlr_disable(struct nvme_controller *ctrlr)
 
 	cc &= ~NVME_CC_REG_EN_MASK;
 	nvme_mmio_write_4(ctrlr, cc, cc);
+
 	/*
-	 * Some drives have issues with accessing the mmio after we
-	 * disable, so delay for a bit after we write the bit to
-	 * cope with these issues.
+	 * A few drives have firmware bugs that freeze the drive if we access
+	 * the mmio too soon after we disable.
 	 */
 	if (ctrlr->quirks & QUIRK_DELAY_B4_CHK_RDY)
 		pause("nvmeR", MSEC_2_TICKS(B4_CHK_RDY_DELAY_MS));