linux-kernel - RE: [PATCH-V2] OMAP: Fix for bus width which improves SD card's peformance.

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Date:	Wed, 31 Mar 2010 11:37:19 -0500
From:	"Madhusudhan" <madhu.cr@...com>
To:	"'kishore kadiyala'" <kishorek.kadiyala@...il.com>,
	"'Vimal Singh'" <vimal.newwork@...il.com>
Cc:	<tony@...mide.com>, <svenkatr@...com>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<jarkko.lavinen@...ia.com>
Subject: RE: [PATCH-V2] OMAP: Fix for bus width which improves SD card's peformance.



> -----Original Message-----
> From: kishore kadiyala [mailto:kishorek.kadiyala@...il.com]
> Sent: Wednesday, March 31, 2010 2:03 AM
> To: Vimal Singh
> Cc: Madhusudhan; tony@...mide.com; svenkatr@...com; linux-
> omap@...r.kernel.org; linux-kernel@...r.kernel.org;
> jarkko.lavinen@...ia.com
> Subject: Re: [PATCH-V2] OMAP: Fix for bus width which improves SD card's
> peformance.
> 
> Sorry for that and here's the Updated one.
> 
> From: Kishore Kadiyala <kishore.kadiyala@...com>
> 
> This patch improves low speeds for SD cards.
> OMAP-MMC controller's can support maximum bus width of '8'.
> when bus width is mentioned as "8" in controller data,the SD
> stack will check whether bus width is "4" and if not it will
> set bus width to "1" and there by degrading performance.
> This patch fixes the issue and improves the performance of
> SD cards.
> 
> Signed-off-by: Kishore Kadiyala <kishore.kadiyala@...com>
> Signed-off-by: Venkatraman S <svenkatr@...com>
> Acked-by: Madhusudhan Chikkature <madhu.cr@...com>
> 
> ---
> In V2 : Appended Signed-off by Venkat and Ack by Madhu
> 
>  Here are my experiment numbers, on a Class 6 SDHC card:
>  Read peformance is increased by 220%
>  Write Performance is increased by 52%
> 
>  drivers/mmc/host/omap_hsmmc.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
> index 83f0aff..8c97c22 100644
> --- a/drivers/mmc/host/omap_hsmmc.c
> +++ b/drivers/mmc/host/omap_hsmmc.c
> @@ -2092,7 +2092,7 @@ static int __init omap_hsmmc_probe(struct
>  		     MMC_CAP_WAIT_WHILE_BUSY;
> 
>  	if (mmc_slot(host).wires >= 8)
> -		mmc->caps |= MMC_CAP_8_BIT_DATA;
> +		mmc->caps |= (MMC_CAP_8_BIT_DATA | MMC_CAP_4_BIT_DATA);
>  	else if (mmc_slot(host).wires >= 4)
>  		mmc->caps |= MMC_CAP_4_BIT_DATA;
> 
Kishore,

Since this patch is not yet pushed it makes sense to fix the readability
issue.

Since 8-bit is the max how about:

        if (mmc_slot(host).wires == 8)
                mmc->caps |= MMC_CAP_8_BIT_DATA | MMC_CAP_4_BIT_DATA;
        if (mmc_slot(host).wires == 4)
                mmc->caps |= MMC_CAP_4_BIT_DATA;

This would be little easy to read the code.

Can you please repost the patch??

Regards,
Madhu

> --
> 1.6.3.3

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