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

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Message-ID: <CANfBPZ-Wb7HE45DTmwsMt-hpJRUevjbjm9-aCR61B4JFULb8Mw@mail.gmail.com>
Date:	Wed, 12 Sep 2012 14:19:51 +0530
From:	"S, Venkatraman" <svenkatr@...com>
To:	"Hebbar, Gururaja" <gururaja.hebbar@...com>
Cc:	linux-omap@...r.kernel.org, linux-mmc@...r.kernel.org,
	rob.herring@...xeda.com, linux-kernel@...r.kernel.org,
	grant.likely@...retlab.ca, cjb@...top.org, nsekhar@...com,
	sudhakar.raj@...com
Subject: Re: [PATCH] mmc: omap_hsmmc: Enable HSPE bit for high speed cards

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.
By definition, HS implies 25MHz or above, so that check seems to be
redundant as well.
Meanwhile, I'll check with HSPE enabled on OMAP.

Regards,
Venkat.
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