Hi Rob > -----Original Message----- > From: Rob Herring <robh@xxxxxxxxxx> > Sent: Wednesday, September 29, 2021 6:28 AM > To: Chin-Ting Kuo <chin-ting_kuo@xxxxxxxxxxxxxx> > 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@xxxxxxxxxxxxxx> wrote: > > > > Hi Rob, > > > > > -----Original Message----- > > > From: Rob Herring <robh@xxxxxxxxxx> > > > Sent: Tuesday, September 28, 2021 2:59 AM > > > To: Chin-Ting Kuo <chin-ting_kuo@xxxxxxxxxxxxxx> > > > 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
