scsi: ufs: qcom: Add a readl() to make sure ref_clk gets enabled
authorManivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Wed, 4 May 2022 08:42:10 +0000 (14:12 +0530)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Thu, 9 Jun 2022 08:26:21 +0000 (10:26 +0200)
commit349c3e9e5d61f2614942caad7bbf04f9799336ea
tree1e0c4230a9716f0b7716c643ad630bc2b9c8c183
parent58e4cbaefe0adfbe69d2e70c37d1227e18c3e200
scsi: ufs: qcom: Add a readl() to make sure ref_clk gets enabled

commit 8eecddfca30e1651dc1c74531ed5eef21dcce7e3 upstream.

In ufs_qcom_dev_ref_clk_ctrl(), it was noted that the ref_clk needs to be
stable for at least 1us. Even though there is wmb() to make sure the write
gets "completed", there is no guarantee that the write actually reached the
UFS device. There is a good chance that the write could be stored in a
Write Buffer (WB). In that case, even though the CPU waits for 1us, the
ref_clk might not be stable for that period.

So lets do a readl() to make sure that the previous write has reached the
UFS device before udelay().

Also, the wmb() after writel_relaxed() is not really needed. Both writel()
and readl() are ordered on all architectures and the CPU won't speculate
instructions after readl() due to the in-built control dependency with read
value on weakly ordered architectures. So it can be safely removed.

Link: https://lore.kernel.org/r/20220504084212.11605-4-manivannan.sadhasivam@linaro.org
Fixes: f06fcc7155dc ("scsi: ufs-qcom: add QUniPro hardware support and power optimizations")
Cc: stable@vger.kernel.org
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/scsi/ufs/ufs-qcom.c