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[RFC,v3,06/11] scsi: ufs: cdns-pltfrm: Perform read back after writing HCLKDIV

Message ID 20231221-ufs-reset-ensure-effect-before-delay-v3-6-2195a1b66d2e@redhat.com
State Superseded
Headers show
Series scsi: ufs: Remove overzealous memory barriers | expand

Commit Message

Andrew Halaney Dec. 21, 2023, 7:09 p.m. UTC 
Currently, HCLKDIV is written to and then 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

Let's do that to ensure the bit hits the device. Because the mb()'s
purpose wasn't to add extra ordering (on top of the ordering guaranteed
by writel()/readl()), it can safely be removed.

Fixes: d90996dae8e4 ("scsi: ufs: Add UFS platform driver for Cadence UFS")
Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
---
 drivers/ufs/host/cdns-pltfrm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
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Patch

diff --git a/drivers/ufs/host/cdns-pltfrm.c b/drivers/ufs/host/cdns-pltfrm.c
index bb30267da471..66811d8d1929 100644
--- a/drivers/ufs/host/cdns-pltfrm.c
+++ b/drivers/ufs/host/cdns-pltfrm.c
@@ -136,7 +136,7 @@  static int cdns_ufs_set_hclkdiv(struct ufs_hba *hba)
 	 * Make sure the register was updated,
 	 * UniPro layer will not work with an incorrect value.
 	 */
-	mb();
+	ufshcd_readl(hba, CDNS_UFS_REG_HCLKDIV);
 
 	return 0;
 }