linux-kernel - Re: [PATCH v4 5/7] scsi: ipr: Eliminate duplicate barriers on weakly-ordered archs

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Date:   Tue, 29 May 2018 15:45:52 -0500
From:   Brian King <brking@...ux.ibm.com>
To:     Sinan Kaya <okaya@...eaurora.org>, linux-scsi@...r.kernel.org,
        timur@...eaurora.org, sulrich@...eaurora.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Brian King <brking@...ibm.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/7] scsi: ipr: Eliminate duplicate barriers on
 weakly-ordered archs

On 03/19/2018 09:50 PM, Sinan Kaya wrote:
> Code includes barrier() followed by writel(). writel() already has a
> barrier
> on some architectures like arm64.
> 
> This ends up CPU observing two barriers back to back before executing the
> register write.
> 
> Since code already has an explicit barrier call, changing writeX() to
> writeX_relaxed().
> 
> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
> ---
>  drivers/scsi/ipr.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/scsi/ipr.c b/drivers/scsi/ipr.c
> index e07dd99..209adac 100644
> --- a/drivers/scsi/ipr.c
> +++ b/drivers/scsi/ipr.c
> @@ -762,9 +762,9 @@ static void ipr_mask_and_clear_interrupts(struct ipr_ioa_cfg *ioa_cfg,
> 
>  	/* Set interrupt mask to stop all new interrupts */
>  	if (ioa_cfg->sis64)
> -		writeq(~0, ioa_cfg->regs.set_interrupt_mask_reg);
> +		writeq_relaxed(~0, ioa_cfg->regs.set_interrupt_mask_reg);
>  	else
> -		writel(~0, ioa_cfg->regs.set_interrupt_mask_reg);
> +		writel_relaxed(~0, ioa_cfg->regs.set_interrupt_mask_reg);
> 
>  	/* Clear any pending interrupts */
>  	if (ioa_cfg->sis64)
> @@ -8435,7 +8435,8 @@ static int ipr_reset_enable_ioa(struct ipr_cmnd *ipr_cmd)
>  	wmb();
>  	if (ioa_cfg->sis64) {
>  		/* Set the adapter to the correct endian mode. */
> -		writel(IPR_ENDIAN_SWAP_KEY, ioa_cfg->regs.endian_swap_reg);
> +		writel_relaxed(IPR_ENDIAN_SWAP_KEY,
> +			       ioa_cfg->regs.endian_swap_reg);
>  		int_reg = readl(ioa_cfg->regs.endian_swap_reg);
>  	}
> 

Looks fine to me. Thanks.

Acked-by: Brian King <brking@...ux.vnet.ibm.com>

-- 
Brian King
Power Linux I/O
IBM Linux Technology Center