Re: [PATCH v3 6/6] mmc: sdhci-esdhc-imx: set back the burst_length_enable bit to 1

[Dong Aisheng <aisheng.dong@freescale.com>]

On Mon, Aug 03, 2015 at 09:08:28AM +0800, Chen Haibo-B51421 wrote:
> 
> 
> > -----Original Message-----
> > From: Dong Aisheng [mailto:aisheng.dong@freescale.com]
> > Sent: Friday, July 31, 2015 10:58 PM
> > To: Chen Haibo-B51421
> > Cc: robh+dt@kernel.org; pawel.moll@arm.com; mark.rutland@arm.com;
> > ijc+devicetree@hellion.org.uk; galak@codeaurora.org; shawnguo@kernel.org;
> > kernel@pengutronix.de; linux@arm.linux.org.uk; ulf.hansson@linaro.org;
> > johan.derycke@barco.com; Estevam Fabio-R49496; Dong Aisheng-B29396;
> > devicetree@vger.kernel.org; linux-kernel@vger.kernel.org; linux-arm-
> > kernel@lists.infradead.org; linux-mmc@vger.kernel.org
> > Subject: Re: [PATCH v3 6/6] mmc: sdhci-esdhc-imx: set back the
> > burst_length_enable bit to 1
> > 
> > On Wed, Jul 29, 2015 at 05:03:57PM +0800, Haibo Chen wrote:
> > > Currently we find that if a usdhc is choosed to boot system, then ROM
> > > code will set the burst length enable bit of this usdhc as 0.
> > >
> > > This will make performance drop a lot if this usdhc's burst length is
> > > 16. So this patch set back the burst_length_enable bit as 1, which is
> > > the default value, and means burst length is enabled for INCR.
> > >
> > > Signed-off-by: Haibo Chen <haibo.chen@freescale.com>
> > > ---
> > >  drivers/mmc/host/sdhci-esdhc-imx.c | 11 +++++++++++
> > >  1 file changed, 11 insertions(+)
> > >
> > > diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c
> > > b/drivers/mmc/host/sdhci-esdhc-imx.c
> > > index 37d0095..dd945e5 100644
> > > --- a/drivers/mmc/host/sdhci-esdhc-imx.c
> > > +++ b/drivers/mmc/host/sdhci-esdhc-imx.c
> > > @@ -32,6 +32,7 @@
> > >  #include "sdhci-esdhc.h"
> > >
> > >  #define	ESDHC_CTRL_D3CD			0x08
> > > +#define ESDHC_BURST_LEN_EN_INCR		(1 << 27)
> > >  /* VENDOR SPEC register */
> > >  #define ESDHC_VENDOR_SPEC		0xc0
> > >  #define  ESDHC_VENDOR_SPEC_SDIO_QUIRK	(1 << 1)
> > > @@ -1158,6 +1159,16 @@ static int sdhci_esdhc_imx_probe(struct
> > platform_device *pdev)
> > >  		host->quirks2 |= SDHCI_QUIRK2_PRESET_VALUE_BROKEN;
> > >  		host->mmc->caps |= MMC_CAP_1_8V_DDR;
> > >
> > > +		/*
> > > +		 * ROM code will change the burst_length_enable setting to
> > > +		 * zero if this usdhc is choosed to boot system. Change it
> > > +		 * back here, otherwise it will impact the performance a
> > > +		 * lot if the burst length is 16.
> > 
> > Can you clarify a bit more on why performance drops a lot if burst length
> > is 16?
> > Caused by the burst length setting did not work due to ROM disabled it?
> 
> 
> [haibo] this bit is used to enable/disable the burst length for the external AHB2AXI bridge, 
> It's useful especially for INCR transfer because without burst length indicator, the AHB2AXI 
> bridge doesn't know the burst length in advance. And without burst length indicator, AHB INCR 
> transfers can only be converted to singles on the AXI side.
> 
> Seting this bit means burst length enabled for INCR.
> If this bit is not set, performance will drop a lot when burst length is 8 or 16. I will add 
> this in the commit log.
>  

Thanks for clarify.
One question: with this patch, can we set the default watermark level to 64 by default for all
SoC types?

If yes, we may not need patch 5 anymore.
[PATCH v3 5/6] mmc: sdhci-esdhc-imx: config watermark level and burst length

Regards
Dong Aisheng

> > 
> > Regards
> > Dong Aisheng
> > 
> > > +		 */
> > > +		writel(readl(host->ioaddr + SDHCI_HOST_CONTROL)
> > > +			| ESDHC_BURST_LEN_EN_INCR,
> > > +			host->ioaddr + SDHCI_HOST_CONTROL);
> > > +
> > >  		if (!(imx_data->socdata->flags & ESDHC_FLAG_HS200))
> > >  			host->quirks2 |= SDHCI_QUIRK2_BROKEN_HS200;
> > >
> > > --
> > > 1.9.1
> > >