linux-kernel - RE: [PATCH v3] OMAP: Fix for bus width which improves SD card's peformance.

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Date:	Tue, 6 Apr 2010 11:16:01 -0500
From:	"Madhusudhan" <madhu.cr@...com>
To:	<me@...ipebalbi.com>
Cc:	"'kishore kadiyala'" <kishorek.kadiyala@...il.com>,
	"'Vimal Singh'" <vimal.newwork@...il.com>, <tony@...mide.com>,
	<svenkatr@...com>, <linux-omap@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <jarkko.lavinen@...ia.com>
Subject: RE: [PATCH v3] OMAP: Fix for bus width which improves SD card's peformance.



> -----Original Message-----
> From: Felipe Balbi [mailto:me@...ipebalbi.com]
> Sent: Tuesday, April 06, 2010 12:01 AM
> To: Madhusudhan
> Cc: me@...ipebalbi.com; 'kishore kadiyala'; 'Vimal Singh';
> tony@...mide.com; svenkatr@...com; linux-omap@...r.kernel.org; linux-
> kernel@...r.kernel.org; jarkko.lavinen@...ia.com
> Subject: Re: [PATCH v3] OMAP: Fix for bus width which improves SD card's
> peformance.
> 
> Hi,
> 
> On Mon, Apr 05, 2010 at 12:19:29PM -0500, Madhusudhan wrote:
> > Since the first if command already checks for the 8-bit the second check
> > like >= 4 is definitely not readable in my opinion.
> 
> how come ???
> 
> > Functionally do you see anything wrong with this patch??
> 
> functionally no, but (hypothetical situation) and if on
> omap4/5/6/whatever, omap controller supports a bigger bus width then
> you'll have to add a line like:
> 
> +	if (mmc_slot(host).wires == 16)
> +		mmc->caps |= (MMC_CAP_16_BIT_DATA | MMC_CAP_8_BIT_DATA |
> +				MMC_CAP_4_BIT_DATA);
> -	if (mmc_slot(host).wires == 8)
> +	else if (mmc_slot(host).wires == 8)
> 
> do you see the problem ?? In my opinion it doesn't scale well.
> 

The point we should note here is that MMC spec supports a max bus width of
8-bit. So anything beyond 8-bit is not in the picture as of today.

But, my bad on miss interpreting the snippet Felipe sent earlier.

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

I missed the fact that you removed the setting of 4-bit from the first
check.

I am okay with the above snippet as it is a trivial change that we are
trying to patch here which fixes an important issue.

Regards,
Madhu
> --
> balbi

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