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scsi: ufs: cdns-pltfrm: Perform read back after writing HCLKDIV
[ Upstream commitb715c55daf
] 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:d90996dae8
("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-v5-6-181252004586@redhat.com 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>
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@ -135,7 +135,7 @@ static int cdns_ufs_set_hclkdiv(struct ufs_hba *hba)
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* Make sure the register was updated,
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* UniPro layer will not work with an incorrect value.
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*/
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mb();
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ufshcd_readl(hba, CDNS_UFS_REG_HCLKDIV);
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return 0;
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}
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