Re: [PATCH v3] OMAP: Fix for bus width which improves SD card's peformance.

From: Felipe Balbi <felipe.balbi@nokia.com>
To: ext Madhusudhan <madhu.cr@ti.com>
Cc: "me@felipebalbi.com" <me@felipebalbi.com>,
	"'kishore kadiyala'" <kishorek.kadiyala@gmail.com>,
	"'Vimal Singh'" <vimal.newwork@gmail.com>,
	"tony@atomide.com" <tony@atomide.com>,
	"svenkatr@ti.com" <svenkatr@ti.com>,
	"linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Lavinen Jarkko (Nokia-D/Helsinki)" <jarkko.lavinen@nokia.com>
Subject: Re: [PATCH v3] OMAP: Fix for bus width which improves SD card's peformance.
Date: Tue, 6 Apr 2010 19:32:11 +0300	[thread overview]
Message-ID: <20100406163211.GA29117@nokia.com> (raw)
In-Reply-To: <003901cad5a4$730264d0$544ff780@am.dhcp.ti.com>

On Tue, Apr 06, 2010 at 06:16:01PM +0200, ext Madhusudhan wrote:
>
>
>> -----Original Message-----
>> From: Felipe Balbi [mailto:me@felipebalbi.com]
>> Sent: Tuesday, April 06, 2010 12:01 AM
>> To: Madhusudhan
>> Cc: me@felipebalbi.com; 'kishore kadiyala'; 'Vimal Singh';
>> tony@atomide.com; svenkatr@ti.com; linux-omap@vger.kernel.org; linux-
>> kernel@vger.kernel.org; jarkko.lavinen@nokia.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.

in that case, the code could be:

WARN_ON(mmc_slot(host).wires > 8);

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;

-- 
balbi