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Date:   Wed, 29 Sep 2021 03:03:43 +0000
From:   Chin-Ting Kuo <chin-ting_kuo@...eedtech.com>
To:     Rob Herring <robh@...nel.org>
CC:     "joel@....id.au" <joel@....id.au>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "sboyd@...nel.org" <sboyd@...nel.org>,
        "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "andrew@...id.au" <andrew@...id.au>,
        BMC-SW <BMC-SW@...eedtech.com>,
        Steven Lee <steven_lee@...eedtech.com>
Subject: RE: [PATCH 10/10] dt-bindings: mmc: aspeed: Add a new compatible
 string

Hi Rob

> -----Original Message-----
> From: Rob Herring <robh@...nel.org>
> Sent: Wednesday, September 29, 2021 6:28 AM
> To: Chin-Ting Kuo <chin-ting_kuo@...eedtech.com>
> Subject: Re: [PATCH 10/10] dt-bindings: mmc: aspeed: Add a new compatible
> string
> 
> On Mon, Sep 27, 2021 at 9:51 PM Chin-Ting Kuo
> <chin-ting_kuo@...eedtech.com> wrote:
> >
> > Hi Rob,
> >
> > > -----Original Message-----
> > > From: Rob Herring <robh@...nel.org>
> > > Sent: Tuesday, September 28, 2021 2:59 AM
> > > To: Chin-Ting Kuo <chin-ting_kuo@...eedtech.com>
> > > Subject: Re: [PATCH 10/10] dt-bindings: mmc: aspeed: Add a new
> > > compatible string
> > >
> > > On Wed, Sep 22, 2021 at 06:31:16PM +0800, Chin-Ting Kuo wrote:
> > > > Add "aspeed,ast2600-emmc" compatible string for the sake of
> > > > distinguishing between SD and eMMC device.
> > >
> > > Why?
> > >
> > > Is the h/w block different? We already have properties to handle
> > > some of the eMMC specifics. Also, you can have a child node for the
> > > eMMC device if you need that.
> >
> > There are two SD/SDIO controllers in a AST2600 SoC.
> > One is for SD card and the other is for eMMC.
> > Although both of them are embedded in the same SoC, the design of
> > delay cell and the manufacture process are different. The delay phase
> > is definitely different and, thus, we need a flag, compatible, to distinguish the
> device, SD or eMMC.
> >
> > Without "aspeed,ast2600-emmc" compatible, of course, eMMC device can
> > work with original sdhci driver and device tree setting. But, for
> > ultra-speed or HS200 case, AST2600 SoC needs some phase delay which
> (maximum) value is different between SD and eMMC device.
> 
> This is quite common as tweaking the timing is also need per board.
> Look at what other bindings have done. A property is more appropriate here.

Okay, I will try to check whether there is an existing binding which can achieve this purpose.
Or, maybe, as you said, a property is better since this phase delay is a proprietary
HW design and is different between each chipset version.

> 
> Rob

Chin-Ting

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