Re: [PATCH RFC v3 07/11] scsi: ufs: core: Perform read back after writing UTP_TASK_REQ_LIST_BASE_H

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On 12/22/2023 3:09 AM, Andrew Halaney wrote:
are 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 these bits have 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:

Let's do that to ensure the bits hit 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: 88441a8d355d ("scsi: ufs: core: Add hibernation callbacks")
Signed-off-by: Andrew Halaney <ahalaney@xxxxxxxxxx>
  drivers/ufs/core/ufshcd.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index d1e33328ff3f..7bfb556e5b8e 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -10351,7 +10351,7 @@ int ufshcd_system_restore(struct device *dev)
  	 * are updated with the latest queue addresses. Only after
  	 * updating these addresses, we can queue the new commands.
-	mb();
+	ufshcd_readl(hba, REG_UTP_TASK_REQ_LIST_BASE_H);
/* Resuming from hibernate, assume that link was OFF */

Reviewed-by: Can Guo <quic_cang@xxxxxxxxxxx>

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