From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
Subject: Re: [RFC PATCH v6 5/5] mmc: queue: Use bigger segments if IOMMU
	can merge the segments
Date: Fri, 14 Jun 2019 09:24:59 +0200
Message-ID: <20190614072459.GD8420@lst.de>
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To: Yoshihiro Shimoda <yoshihiro.shimoda.uh-zM6kxYcvzFBBDgjK7y7TUQ@public.gmane.org>
Cc: axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org, linux-renesas-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, ulf.hansson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, linux-mmc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, wsa+renesas-jBu1N2QxHDJrcw3mvpCnnVaTQe2KTcn/@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, hch-jcswGhMUV9g@public.gmane.org
List-Id: linux-mmc@vger.kernel.org

On Thu, Jun 13, 2019 at 07:20:15PM +0900, Yoshihiro Shimoda wrote:
> +static unsigned int mmc_get_max_segments(struct mmc_host *host)
> +{
> +	return host->can_merge ? BLK_MAX_SEGMENTS : host->max_segs;
> +}

Note that BLK_MAX_SEGMENTS is really a little misnamed, it just
is a BLK_DEFAULT_SEGMENTS.  I think you are better of picking your
own value here (even if 128 ends up ok) than reusing this somewhat
confusing constant.

> +	/*
> +	 * Since blk_mq_alloc_tag_set() calls .init_request() of mmc_mq_ops,
> +	 * the host->can_merge should be set before to get max_segs from
> +	 * mmc_get_max_segments().
> +	 */
> +	if (host->max_segs < BLK_MAX_SEGMENTS &&
> +	    device_iommu_mapped(mmc_dev(host)))
> +		host->can_merge = 1;
> +	else
> +		host->can_merge = 0;
> +

can_merge seems a little too generic a name to me.  Maybe can_iommu_merge?