linux-kernel - Re: [RFC PATCH] mmc: sprd: add MMC host driver for Spreadtrum SoC

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Date:	Fri, 3 Jul 2015 10:50:19 +0800
From:	Orson Zhai <orsonzhai@...il.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Chunyan Zhang <chunyan.zhang@...eadtrum.com>,
	"chris@...ntf.net" <chris@...ntf.net>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Lee Jones <lee.jones@...aro.org>,
	Shawn Guo <shawn.guo@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Arnd Bergmann <arnd@...db.de>, billows.wu@...eadtrum.com,
	Wei Qiao (乔伟) <wei.qiao@...eadtrum.com>,
	baolin.wang@...eadtrum.com, ning.yang@...eadtrum.com,
	Orson Zhai(翟京) <orson.zhai@...eadtrum.com>,
	jason.wu@...eadtrum.com,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [RFC PATCH] mmc: sprd: add MMC host driver for Spreadtrum SoC

On Thu, Jul 2, 2015 at 11:47 PM, Rob Herring <robherring2@...il.com> wrote:
> On Thu, Jul 2, 2015 at 4:26 AM, Orson Zhai <orsonzhai@...il.com> wrote:
>> Hi Rob,
>>
>> Thanks for your quick reply.
>> I have one question to your last comment.
>>
>> On Thu, Jul 2, 2015 at 1:50 AM, Rob Herring <robherring2@...il.com> wrote:
>>> On Wed, Jul 1, 2015 at 2:23 AM, Chunyan Zhang
>>> <chunyan.zhang@...eadtrum.com> wrote:
>>>> From: Billows Wu <billows.wu@...eadtrum.com>
>
> [...]
>
>>>> +const struct of_device_id sdhost_of_match[] = {
>>>> +       {.compatible = "sprd,sd-sdhost-3.0", .data = &sd_caps_info,},
>>>> +       {.compatible = "sprd,wifi-sdhost-3.0", .data = &wifi_caps_info,},
>>>> +       {.compatible = "sprd,emmc-sdhost-3.0",  .data = &emmc_caps_info,},
>>>
>>> What these are connected to is irrelevant to the driver and compatible
>>> string. All these differences belong in the DT unless the IP blocks
>>> are really different.
>>
>> It's my idea to let Billows do like this.
>> I learn from SSP part in freescale  "arch/arm/boot/dts/imx28-evk.dts"
>> Their ssp0-ssp2 each have 2 roles, mmc or generic spi bus.
>> And they may write one of their combo configuration like this:
>
> That is a bit different as the host controller is operating in
> completely different modes. In your case, the host controller is the
> same and functions the same way, but just has different cards
> attached.
>
>>
>>  43                         ssp1: ssp@...12000 {
>>  44                                 compatible = "fsl,imx28-mmc";
>>  45                                 bus-width = <8>;
>>  46                                 wp-gpios = <&gpio0 28 0>;
>>  47                         };
>>  48
>>  49                         ssp2: ssp@...14000 {
>>  50                                 #address-cells = <1>;
>>  51                                 #size-cells = <0>;
>>  52                                 compatible = "fsl,imx28-spi";
>>  53                                 pinctrl-names = "default";
>>  54                                 pinctrl-0 = <&spi2_pins_a>;
>>  55                                 status = "okay";
>>  56
>>  57                                 flash: m25p80@0 {
>>  58                                         #address-cells = <1>;
>>  59                                         #size-cells = <1>;
>>  60                                         compatible = "sst,sst25vf016b";
>>  61                                         spi-max-frequency = <40000000>;
>>  62                                         reg = <0>;
>>  63                                 };
>>  64                         };
>>
>> Billows tell me they also have 3 roles in their sd host controller
>> corresponding to 3 kinds of different operation.
>> He used to create "sprd,name" property for this. Is it a good way or
>> anything else better?
>
> Why do you need to know? You can define parameters which can't be
> probed such as bus width, voltage, and clock freq. in DT for each
> host. The MMC subsys core will figure out the type of device attached.

I think you're right.
Thanks!
-orson

>
> Rob
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