scsi: ipr: Eliminate duplicate barriers

Driver does both wmb() and writel(). The latter already has a barrier
on some architectures like arm64. This ends up with CPU observing two
barriers back to back before executing the register write.

Drivers should generally assume that the barrier implied by writel() is
sufficient for ordering DMA. Remove the extraneous wmb() before it.

[mkp: Squashed Arnd's and Sinan's patches]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reported-by: Sinan Kaya <okaya@codeaurora.org>
Acked-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/ipr.c

@@ -760,7 +760,6 @@ static void ipr_mask_and_clear_interrupts(struct ipr_ioa_cfg *ioa_cfg,
 		ioa_cfg->hrrq[i].allow_interrupts = 0;
 		spin_unlock(&ioa_cfg->hrrq[i]._lock);
 	}
-	wmb();
 
 	/* Set interrupt mask to stop all new interrupts */
 	if (ioa_cfg->sis64)
@@ -8403,7 +8402,6 @@ static int ipr_reset_enable_ioa(struct ipr_cmnd *ipr_cmd)
 		ioa_cfg->hrrq[i].allow_interrupts = 1;
 		spin_unlock(&ioa_cfg->hrrq[i]._lock);
 	}
-	wmb();
 	if (ioa_cfg->sis64) {
 		/* Set the adapter to the correct endian mode. */
 		writel(IPR_ENDIAN_SWAP_KEY, ioa_cfg->regs.endian_swap_reg);