Re: [RFC PATCH v7 5/5] mmc: queue: Use bigger segments if DMA MAP layer can merge the segments

From: Ulf Hansson <ulf.hansson@linaro.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Robin Murphy <robin.murphy@arm.com>,
	"list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
	Joerg Roedel <joro@8bytes.org>," <joro@8bytes.org>,
	Jens Axboe <axboe@kernel.dk>,
	Wolfram Sang <wsa+renesas@sang-engineering.com>,
	"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
	"list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>,
	Joerg Roedel <joro@8bytes.org>,"
	<iommu@lists.linux-foundation.org>,
	linux-block <linux-block@vger.kernel.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>
Subject: Re: [RFC PATCH v7 5/5] mmc: queue: Use bigger segments if DMA MAP layer can merge the segments
Date: Mon, 8 Jul 2019 13:45:50 +0200	[thread overview]
Message-ID: <CAPDyKFpuRzmZUK730FMnh0hf3WRFb9aA=o9ciNt2ei8n803vsQ@mail.gmail.com> (raw)
In-Reply-To: <20190624062414.GD2989@lst.de>

On Mon, 24 Jun 2019 at 08:24, Christoph Hellwig <hch@lst.de> wrote:
>
> On Thu, Jun 20, 2019 at 05:50:10PM +0900, Yoshihiro Shimoda wrote:
> > When the max_segs of a mmc host is smaller than 512, the mmc
> > subsystem tries to use 512 segments if DMA MAP layer can merge
> > the segments, and then the mmc subsystem exposes such information
> > to the block layer by using blk_queue_can_use_dma_map_merging().
> >
> > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
> > ---
> >  drivers/mmc/core/queue.c | 35 ++++++++++++++++++++++++++++++++---
> >  include/linux/mmc/host.h |  1 +
> >  2 files changed, 33 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/mmc/core/queue.c b/drivers/mmc/core/queue.c
> > index 92900a0..ab0ecc6 100644
> > --- a/drivers/mmc/core/queue.c
> > +++ b/drivers/mmc/core/queue.c
> > @@ -24,6 +24,8 @@
> >  #include "card.h"
> >  #include "host.h"
> >
> > +#define MMC_DMA_MAP_MERGE_SEGMENTS   512
> > +
> >  static inline bool mmc_cqe_dcmd_busy(struct mmc_queue *mq)
> >  {
> >       /* Allow only 1 DCMD at a time */
> > @@ -196,6 +198,12 @@ static void mmc_queue_setup_discard(struct request_queue *q,
> >               blk_queue_flag_set(QUEUE_FLAG_SECERASE, q);
> >  }
> >
> > +static unsigned int mmc_get_max_segments(struct mmc_host *host)
> > +{
> > +     return host->can_dma_map_merge ? MMC_DMA_MAP_MERGE_SEGMENTS :
> > +                                      host->max_segs;
>
> I personally don't like superflous use of ? : if an if would be more
> obvious:
>
>         if (host->can_dma_map_merge)
>                 return MMC_DMA_MAP_MERGE_SEGMENTS;
>         return host->max_segs;
>
> but that is really just a nitpick and for the mmc maintainer to decide.

I have no strong opinions, both formats are used in mmc code, so I am
fine as is.

>
> Otherwise looks good:
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

Kind regards
Uffe