RE: [PATCH 10/10] dt-bindings: mmc: aspeed: Add a new compatible string - Chin-Ting Kuo

From: Chin-Ting Kuo <chin-ting_kuo@aspeedtech.com>
To: Rob Herring <robh@kernel.org>
Cc: "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linux-clk@vger.kernel.org" <linux-clk@vger.kernel.org>,
	"linux-aspeed@lists.ozlabs.org" <linux-aspeed@lists.ozlabs.org>,
	BMC-SW <BMC-SW@aspeedtech.com>,
	"sboyd@kernel.org" <sboyd@kernel.org>,
	Steven Lee <steven_lee@aspeedtech.com>,
	"openbmc@lists.ozlabs.org" <openbmc@lists.ozlabs.org>,
	"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
	"adrian.hunter@intel.com" <adrian.hunter@intel.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"andrew@aj.id.au" <andrew@aj.id.au>,
	"mturquette@baylibre.com" <mturquette@baylibre.com>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: RE: [PATCH 10/10] dt-bindings: mmc: aspeed: Add a new compatible string
Date: Wed, 29 Sep 2021 03:03:43 +0000	[thread overview]
Message-ID: <HK0PR06MB278642C55052360B039853FAB2A99@HK0PR06MB2786.apcprd06.prod.outlook.com> (raw)
In-Reply-To: <CAL_Jsq+TZFXrvfJTjofVcnT6jJat-3SvWj+jAq0QST8ndfeUMA@mail.gmail.com>

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
> <chin-ting_kuo@aspeedtech.com> wrote:
> >
> > Hi Rob,
> >
> > > -----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:
> > > > 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