5.4-stable review patch. If anyone has any objections, please let me know.
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From: Andrew Halaney ahalaney@redhat.com
[ Upstream commit b715c55daf598aac8fa339048e4ca8a0916b332e ]
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: d90996dae8e4 ("scsi: ufs: Add UFS platform driver for Cadence UFS") Reviewed-by: Manivannan Sadhasivam manivannan.sadhasivam@linaro.org Signed-off-by: Andrew Halaney ahalaney@redhat.com Link: https://lore.kernel.org/r/20240329-ufs-reset-ensure-effect-before-delay-v5-6... Reviewed-by: Bart Van Assche bvanassche@acm.org Signed-off-by: Martin K. Petersen martin.petersen@oracle.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/scsi/ufs/cdns-pltfrm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/scsi/ufs/cdns-pltfrm.c b/drivers/scsi/ufs/cdns-pltfrm.c index 6feeb0faf123a..9d6bb47168706 100644 --- a/drivers/scsi/ufs/cdns-pltfrm.c +++ b/drivers/scsi/ufs/cdns-pltfrm.c @@ -56,7 +56,7 @@ 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; }