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Message-ID: <5f79d8e7-0035-cfb0-d612-3e1c7f243f22@opensource.wdc.com>
Date:   Fri, 1 Jul 2022 08:41:39 +0900
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Subject: Re: [PATCH v5 3/5] scsi: core: Cap shost max_sectors according to DMA
 limits only once
Content-Language: en-US
To:     John Garry <john.garry@huawei.com>, joro@8bytes.org,
        will@kernel.org, jejb@linux.ibm.com, martin.petersen@oracle.com,
        hch@lst.de, m.szyprowski@samsung.com, robin.murphy@arm.com
Cc:     linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-ide@vger.kernel.org, iommu@lists.linux-foundation.org,
        iommu@lists.linux.dev, linux-scsi@vger.kernel.org,
        linuxarm@huawei.com
References: <1656590892-42307-1-git-send-email-john.garry@huawei.com>
 <1656590892-42307-4-git-send-email-john.garry@huawei.com>
From:   Damien Le Moal <damien.lemoal@opensource.wdc.com>
Organization: Western Digital Research
In-Reply-To: <1656590892-42307-4-git-send-email-john.garry@huawei.com>
Content-Type: text/plain; charset=UTF-8
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Precedence: bulk

On 6/30/22 21:08, John Garry wrote:
> The shost->max_sectors is repeatedly capped according to the host DMA
> mapping limit for each sdev in __scsi_init_queue(). This is unnecessary, so
> set only once when adding the host.
> 
> Signed-off-by: John Garry <john.garry@huawei.com>
> ---
>  drivers/scsi/hosts.c    | 5 +++++
>  drivers/scsi/scsi_lib.c | 4 ----
>  2 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> index 8352f90d997d..d04bd2c7c9f1 100644
> --- a/drivers/scsi/hosts.c
> +++ b/drivers/scsi/hosts.c
> @@ -236,6 +236,11 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
>  
>  	shost->dma_dev = dma_dev;
>  
> +	if (dma_dev->dma_mask) {
> +		shost->max_sectors = min_t(unsigned int, shost->max_sectors,
> +				dma_max_mapping_size(dma_dev) >> SECTOR_SHIFT);
> +	}

Nit: you could remove the curly brackets... But it being a multi-line
statement, having them is OK too I think.

> +
>  	error = scsi_mq_setup_tags(shost);
>  	if (error)
>  		goto fail;
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 6ffc9e4258a8..6ce8acea322a 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1884,10 +1884,6 @@ void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
>  		blk_queue_max_integrity_segments(q, shost->sg_prot_tablesize);
>  	}
>  
> -	if (dev->dma_mask) {
> -		shost->max_sectors = min_t(unsigned int, shost->max_sectors,
> -				dma_max_mapping_size(dev) >> SECTOR_SHIFT);
> -	}
>  	blk_queue_max_hw_sectors(q, shost->max_sectors);
>  	blk_queue_segment_boundary(q, shost->dma_boundary);
>  	dma_set_seg_boundary(dev, shost->dma_boundary);

Looks good.

Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

-- 
Damien Le Moal
Western Digital Research