Hi Rob

-----Original Message-----
From: Rob Herring <robh@kernel.org>
Sent: Wednesday, September 29, 2021 6:28 AM
To: Chin-Ting Kuo <chin-ting_kuo@aspeedtech.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
[off-list ref] wrote:

quoted

Hi Rob,

quoted

-----Original Message-----
From: Rob Herring <robh@kernel.org>
Sent: Tuesday, September 28, 2021 2:59 AM
To: Chin-Ting Kuo <chin-ting_kuo@aspeedtech.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:

quoted

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.

quoted

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