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 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?

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
>