RE: [PATCH v2 2/2] mmc: renesas_sdhi: use multiple segments if possible

From: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
To: Wolfram Sang <wsa@the-dreams.de>
Cc: "ulf.hansson@linaro.org" <ulf.hansson@linaro.org>,
	"wsa+renesas@sang-engineering.com"
	<wsa+renesas@sang-engineering.com>,
	"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
	"linux-renesas-soc@vger.kernel.org" 
	<linux-renesas-soc@vger.kernel.org>
Subject: RE: [PATCH v2 2/2] mmc: renesas_sdhi: use multiple segments if possible
Date: Tue, 14 May 2019 06:05:34 +0000	[thread overview]
Message-ID: <OSBPR01MB3174B26541C20C2951509DC8D8080@OSBPR01MB3174.jpnprd01.prod.outlook.com> (raw)
In-Reply-To: <OSBPR01MB3174B96296BFFA408F1C901FD80F0@OSBPR01MB3174.jpnprd01.prod.outlook.com>

Hi Wolfram-san again,

> From: Yoshihiro Shimoda, Sent: Monday, May 13, 2019 6:46 PM
> 
> Hi Wolfram-san,
> 
> > From: Wolfram Sang, Sent: Monday, May 13, 2019 6:01 PM
> >
> > Hi Shimoda-san,
> >
> > thank you for this update!
> >
> > > +static void renesas_sdhi_init_card(struct mmc_host *mmc, struct mmc_card *card)
> > > +{
> > > +	struct tmio_mmc_host *host = mmc_priv(mmc);
> > > +
> > > +	if (host->pdev->dev.iommu_group &&
> >
> > I wonder if I am too cautious, but maybe we should have another
> > condition here to be checked first, namely "host->mmc->max_segs < 512"?
> 
> I got it. I'll fix it on v3 patch.

I'm afraid but I misunderstood this condition is "host->pdata->max_segs", not "host->mmc->max_segs",
to avoid small max_segs value than pdata->max_segs? (No one has such max_segs value at the moment though.)

If we use "host->mmc->max_segs", the max_segments value will be toggled by connecting/disconnecting a card like below:

(a card is connected)
# cat /sys/block/mmcblk0/queue/max_segments
512
(a card is disconnected and connected again)
# cat /sys/block/mmcblk0/queue/max_segments
1
(a card is disconnected and connected again)
# cat /sys/block/mmcblk0/queue/max_segments
512
...

Best regards,
Yoshihiro Shimoda

> > > +	    (mmc_card_mmc(card) || mmc_card_sd(card)))
> > > +		host->mmc->max_segs = 512;
> > > +	else
> > > +		host->mmc->max_segs = host->pdata->max_segs;
> >
> > max_segs can be 0, so we should probably have:
> >
> >  +		host->mmc->max_segs = host->pdata->max_segs ?: 32;
> 
> Thank you for the point! I'll fix it on v3 patch.
> 
> > That also means, for the sys-dmac and Gen2, we then use 512 for the
> > IOMMU case and 32 (default TMIO value) for the non IOMMU case. My
> > understanding is that SYS DMAC can handle 512 in both cases. Maybe it
> > makes sense then to make an incremental patch setting the max_segs value
> > explicitly to 512 in the sys-dmac driver for Gen2?
> 
> I also think SYS DMAC can handle 512 segments. However, I'm not sure
> it can improve the performance or not though. Anyway, an incremental patch
> makes sense if needed, I think.
> 
> Best regards,
> Yoshihiro Shimoda
> 
> > Kind regards,
> >
> >    Wolfram