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

From: Nishanth Menon
Date: Tue Apr 06 2010 - 12:55:28 EST

Felipe Balbi had written, on 04/06/2010 11:32 AM, the following:
On Tue, Apr 06, 2010 at 06:16:01PM +0200, ext Madhusudhan wrote:

-----Original Message-----
From: Felipe Balbi [mailto:me@xxxxxxxxxxxxxxx]
Sent: Tuesday, April 06, 2010 12:01 AM
To: Madhusudhan
Cc: me@xxxxxxxxxxxxxxx; 'kishore kadiyala'; 'Vimal Singh';
tony@xxxxxxxxxxx; svenkatr@xxxxxx; linux-omap@xxxxxxxxxxxxxxx; linux-
kernel@xxxxxxxxxxxxxxx; jarkko.lavinen@xxxxxxxxx
Subject: Re: [PATCH v3] OMAP: Fix for bus width which improves SD card's


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 |
- 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;

some reasons why i love switch statements ;) since I dont expect other than precisely 4 and 8 (do we expect 5,6,7 - i might be wrong).. but if it is so, wont the following be better?

switch (mmc_slot(host).wires)
case 8:
mmc->caps |= MMC_CAP_8_BIT_DATA;
/* fall thru*/
case 4:
mmc->caps |= MMC_CAP_4_BIT_DATA;
WARN("bad width");
Nishanth Menon
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