> From arch/arm/include/asm/io.h
>
> #define __iowmb() wmb()
> [ ... ]
> #define writel(v,c) ({ __iowmb(); writel_relaxed(v,c); })
>
> From Documentation/memory-barriers.txt: "Note that, when using writel(),
> a
> prior wmb() is not needed to guarantee that the cache coherent memory
> writes have completed before writing to the MMIO region."
>
> In other words, calling wmb() before writel() is not necessary. Hence
> remove the wmb() calls that precede a writel() call. Remove the wmb()
> calls that precede a ufshcd_send_command() call since the latter function
> uses writel(). Remove the wmb() call from ufshcd_wait_for_dev_cmd()
> since the following chain of events guarantees that the CPU will see
> up-to-date LRB values:
> * UFS controller writes to host memory.
> * UFS controller posts completion interrupt after the memory writes from
> the previous step are visible to the CPU.
> * complete(hba->dev_cmd.complete) is called from the UFS interrupt
> handler.
> * The wait_for_completion(hba->dev_cmd.complete) call in
> ufshcd_wait_for_dev_cmd() returns.
>
> Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> Cc: Stanley Chu <stanley.chu@xxxxxxxxxxxx>
> Cc: Can Guo <cang@xxxxxxxxxxxxxx>
> Cc: Asutosh Das <asutoshd@xxxxxxxxxxxxxx>
> Cc: Avri Altman <avri.altman@xxxxxxx>
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
Reviewed-by: Avri Altman <avri.altman@xxxxxxx>
Tested-by: Avri altman <avri.altman@xxxxxxx>
> ---
> drivers/scsi/ufs/ufshcd.c | 11 -----------
> 1 file changed, 11 deletions(-)
>
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index f467630be7df..d1c3a984d803 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -2769,8 +2769,6 @@ static int ufshcd_queuecommand(struct Scsi_Host
> *host, struct scsi_cmnd *cmd)
> ufshcd_release(hba);
> goto out;
> }
> - /* Make sure descriptors are ready before ringing the doorbell */
> - wmb();
>
> ufshcd_send_command(hba, tag);
> out:
> @@ -2880,8 +2878,6 @@ static int ufshcd_wait_for_dev_cmd(struct ufs_hba
> *hba,
> time_left = wait_for_completion_timeout(hba->dev_cmd.complete,
> msecs_to_jiffies(max_timeout));
>
> - /* Make sure descriptors are ready before ringing the doorbell */
> - wmb();
> spin_lock_irqsave(hba->host->host_lock, flags);
> hba->dev_cmd.complete = NULL;
> if (likely(time_left)) {
> @@ -2960,8 +2956,6 @@ static int ufshcd_exec_dev_cmd(struct ufs_hba
> *hba,
> hba->dev_cmd.complete = &wait;
>
> ufshcd_add_query_upiu_trace(hba, UFS_QUERY_SEND, lrbp-
> >ucd_req_ptr);
> - /* Make sure descriptors are ready before ringing the doorbell */
> - wmb();
>
> ufshcd_send_command(hba, tag);
> err = ufshcd_wait_for_dev_cmd(hba, lrbp, timeout);
> @@ -6521,9 +6515,6 @@ static int __ufshcd_issue_tm_cmd(struct ufs_hba
> *hba,
> /* send command to the controller */
> __set_bit(task_tag, &hba->outstanding_tasks);
>
> - /* Make sure descriptors are ready before ringing the task doorbell */
> - wmb();
> -
> ufshcd_writel(hba, 1 << task_tag, REG_UTP_TASK_REQ_DOOR_BELL);
> /* Make sure that doorbell is committed immediately */
> wmb();
> @@ -6695,8 +6686,6 @@ static int ufshcd_issue_devman_upiu_cmd(struct
> ufs_hba *hba,
> hba->dev_cmd.complete = &wait;
>
> ufshcd_add_query_upiu_trace(hba, UFS_QUERY_SEND, lrbp-
> >ucd_req_ptr);
> - /* Make sure descriptors are ready before ringing the doorbell */
> - wmb();
>
> ufshcd_send_command(hba, tag);
> /*
