Commit b715c55d authored by Andrew Halaney's avatar Andrew Halaney Committed by Martin K. Petersen
Browse files

scsi: ufs: cdns-pltfrm: Perform read back after writing HCLKDIV 

Currently, HCLKDIV is written to and then completed with an mb().

mb() ensures 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: d90996da ("scsi: ufs: Add UFS platform driver for Cadence UFS")
Reviewed-by: default avatarManivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: default avatarAndrew Halaney <ahalaney@redhat.com>
Link: https://lore.kernel.org/r/20240329-ufs-reset-ensure-effect-before-delay-v5-6-181252004586@redhat.com


Reviewed-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
parent d9488511

drivers/ufs/host/cdns-pltfrm.c

+1 −1
Original line number Diff line number Diff line
@@ -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;

}