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[RFC,v4,03/11] scsi: ufs: qcom: Remove unnecessary mb() after writing testbus config

Message ID 20240122-ufs-reset-ensure-effect-before-delay-v4-3-6c48432151cc@redhat.com (mailing list archive)
State Not Applicable
Headers show
Series scsi: ufs: Remove overzealous memory barriers | expand

Commit Message

Andrew Halaney Jan. 22, 2024, 5:21 p.m. UTC 
Currently, the testbus configuration is written and completed with an
mb().

mb() ensure that the write completes, but completion doesn't mean
that it isn't stored in a buffer somewhere. The recommendation for
ensuring this bit has taken effect on the device is to perform a read
back to force it to make it all the way to the device. This is
documented in device-io.rst and a talk by Will Deacon on this can
be seen over here:

    https://youtu.be/i6DayghhA8Q?si=MiyxB5cKJXSaoc01&t=1678

But, there's really no reason to even ensure completion before
continuing. The only requirement here is that this write is ordered to
this endpoint (which readl()/writel() guarantees already). For that
reason the mb() can be dropped altogether without anything forcing
completion.

Fixes: 9c46b8676271 ("scsi: ufs-qcom: dump additional testbus registers")
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
---
 drivers/ufs/host/ufs-qcom.c | 5 -----
 1 file changed, 5 deletions(-)
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Patch

diff --git a/drivers/ufs/host/ufs-qcom.c b/drivers/ufs/host/ufs-qcom.c
index 0603a07a23a2..a489c8c6f849 100644
--- a/drivers/ufs/host/ufs-qcom.c
+++ b/drivers/ufs/host/ufs-qcom.c
@@ -1429,11 +1429,6 @@  int ufs_qcom_testbus_config(struct ufs_qcom_host *host)
 		    (u32)host->testbus.select_minor << offset,
 		    reg);
 	ufs_qcom_enable_test_bus(host);
-	/*
-	 * Make sure the test bus configuration is
-	 * committed before returning.
-	 */
-	mb();
 
 	return 0;
 }