linux-kernel - Re: [PATCH] mmc: omap_hsmmc: Enable HSPE bit for high speed cards

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Date:	Thu, 27 Sep 2012 13:01:14 +0200
From:	Koen Kooi <koen@...inion.thruhere.net>
To:	"Hebbar, Gururaja" <gururaja.hebbar@...com>
Cc:	"S, Venkatraman" <svenkatr@...com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"grant.likely@...retlab.ca" <grant.likely@...retlab.ca>,
	"cjb@...top.org" <cjb@...top.org>, "Nori, Sekhar" <nsekhar@...com>,
	"Rajashekhara, Sudhakar" <sudhakar.raj@...com>
Subject: Re: [PATCH] mmc: omap_hsmmc: Enable HSPE bit for high speed cards


Op 26 sep. 2012, om 13:37 heeft "Hebbar, Gururaja" <gururaja.hebbar@...com> het volgende geschreven:

> On Wed, Sep 12, 2012 at 17:32:38, Hebbar, Gururaja wrote:
>> On Wed, Sep 12, 2012 at 14:19:51, S, Venkatraman wrote:
>>> On Tue, Sep 4, 2012 at 6:39 PM, Hebbar, Gururaja <gururaja.hebbar@...com> wrote:
>>>> HSMMC IP on AM33xx need a special setting to handle High-speed cards.
>>>> Other platforms like TI81xx, OMAP4 may need this as-well. This depends
>>>> on the HSMMC IP timing closure done for the high speed cards.
>>>> 
>>>> From AM335x TRM (SPRUH73F - 18.3.12 Output Signals Generation)
>>>> 
>>>> The MMC/SD/SDIO output signals can be driven on either falling edge or
>>>> rising edge depending on the SD_HCTL[2] HSPE bit. This feature allows
>>>> to reach better timing performance, and thus to increase data transfer
>>>> frequency.
>>>> 
>>>> There are few pre-requisites for enabling the HSPE bit
>>>> - Controller should support High-Speed-Enable Bit and
>>>> - Controller should not be using DDR Mode and
>>>> - Controller should advertise that it supports High Speed in
>>>>  capabilities register and
>>>> - MMC/SD clock coming out of controller > 25MHz
>>>> 
>>> 
>>> The patch is well written. But then, I don't see a need for a DT
>>> binding for this feature.
>> 
>> My reasons for DT Binding
>> 1. Not all platforms using this driver has this bit (OMAP2)
>> 2. Not all platforms using this driver needs this bit to be enabled (OMAP4)
>> 3. Platforms which require this bit this to be set needs a method to inform 
>> driver.
>> 
>> In order to not disturb old/unsupported platforms, I chose this DT method.
>> 
>>> By definition, HS implies 25MHz or above, so that check seems to be
>>> redundant as well.
>> 
>> There are chances that the platform Max Clock output from HSMMC IP is < than 
>> 25 MHz even if the card is High Speed. In such cases it would be better to
>> Confirm that the Clock output is actually > 25 MHz
>> 
>> Kindly correct me if I am wrong.
>> 
>>> Meanwhile, I'll check with HSPE enabled on OMAP.
>>> 
> 
> Gentle Ping. 
> 
> Matt Poter recently submitted EDMA related patches as RFC. He confirmed that
> basic mmc is working on AM335x with his edma patches. 
> 
> Above patch is required to get High-speed cards working on AM335x.
> 
> I haven't seen any review comments for this. Can this be pulled in for 3.7?

I had trouble applying this to 3.6-rc7, is that a known problem and should I try linux-next?

regards,

Koen--
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