Subject: Where to power on the wifi device before loading the driver.

From: [email-masked] (Rob Herring)
Date: Tue, 26 Jun 2012 16:26:04 -0500

On 06/26/2012 11:53 AM, Stephen Warren wrote:
> (I'm adding everyone on thread "ARM: imx6q: add config-on-boot gpios" to
> the CC of this similar thread. Sorry if you think that's spam.)
> 
> On 06/26/2012 02:56 AM, Dong Aisheng wrote:
>> On Tue, Jun 19, 2012 at 06:01:54PM -0600, Stephen Warren wrote:
> ...
>>> I think what we need is some way of matching a DT node to a device even
>>> when that device was instantiated through some probing mechanism such as
>>> SDIO or USB (and I've heard hints that one can already do this for PCI;
>>> I should investigate).
>>>
>>> So, we start off with the plain SDHCI controller node:
>>>
>>> sdhci at 78000000 {
>>> 	compatible = "nvidia,tegra30-sdhci", "nvidia,tegra20-sdhci";
>>> 	reg = <0x78000000 0x200>;
>>> 	interrupts = <0 14 0x04>;
>>> };
>>>
>>> Then, we add a child node to represent the device that's attached:
>>>
>>> sdhci at 78000000 {
>>> 	compatible = "nvidia,tegra30-sdhci", "nvidia,tegra20-sdhci";
>>> 	reg = <0x78000000 0x200>;
>>> 	interrupts = <0 14 0x04>;
>>>
>>> 	sdio-device {
>>> 		reset-gpios = <...>;
>>> 		enable-gpios = <...>;
>>> 	};
>>> };
>>>
>>> When the SDHCI controller/core instantiates the child device it finds on
>>> the HW bus, it initializes that struct device's of_node with a pointer
>>> to the sdio-device node above. From there, the child device can get DT
>>> properties such as GPIOs in the usual way.
>>>
>>> However, there are still some issues that need thought here; what if (as
>>> is I believe the case on Cardhu) we can in fact plug in multiple
>>> different types of device into the socket? Might we end up with
>>> something like:
>>>
>>> sdhci at 78000000 {
>>> 	compatible = "nvidia,tegra30-sdhci", "nvidia,tegra20-sdhci";
>>> 	reg = <0x78000000 0x200>;
>>> 	interrupts = <0 14 0x04>;
>>>
>>> 	sdio-device-option at 0 {
>>> 		compatible = "broadcom,bcm4239";
>>> 		reset-gpios = <...>;
>>> 		enable-gpios = <...>;
>>> 	};
>>>
>>> 	sdio-device-option at 1 {
>>> 		compatible = "broadcom,bcm4330";
>>> 		reset-gpios = <...>;
>>> 		enable-gpios = <...>;
>>> 	};
>>> };
>>>
>>> and match on compatible value?
>>>
>> I like this idea.
>> We may extend the sdio_device_id to contain a compatible string,
>> then sdio core is responsible to pass the corresponding device node to the
>> sdio function driver once a match device found, this is sdio function independent.
>> The sdio function driver then are responsible to parse the device node to
>> fetch the needed information like reset-gpios and enable-gpios to do correct
>> initialization sequence.
>>
>> However, one known question for this model is that some WiFi may need reset the chip
>> via gpio first before being able to be enumerated.
> 
> Yes, that's exactly the issue that makes the above binding incorrect.
> 
> In another thread on a very similar topic, I proposed a binding that
> would address this issue:
> 
> http://www.spinics.net/lists/linux-usb/msg66013.html
> 
>> sdhci at 78000000 {
>> 	compatible = "nvidia,tegra30-sdhci", "nvidia,tegra20-sdhci";
>> 	reg = <0x78000000 0x200>;
>> 	interrupts = <0 14 0x04>;
>>
>> 	sdio-device {
>> 		reset-gpios = <...>;
>> 		enable-gpios = <...>;
>> 	};

These are really no different than CD and WP on gpio lines. So I don't
think a child node is even necessary. They are really properties of the
host controller as you have to know how to handle them before enumeration.

One question is do the gpios have strict timing or ordering
requirements. If so then that would be difficult to describe generically.

>> };
> 
>> ehci {
>>     /* The following node is dynamically detected, although the hub
>>      * IC is physically soldered onto the board
>>      */
>>     hub {
>>         hub { /* also dynamic */
>>             port at 2 {
>>                 child-supply = <&regulator>;
>>                 reset-gpios = <&gpio 0 0>;
>>             };
>>         };
>>     };
>> }
> 

Considering the same enumeration ordering requirement as above and that
this is probably limited to a single hub/device on the root hub, I think
the simple solution of just adding the gpio's to the ehci node and
handling in the ehci driver is sufficient.

> Presumably something similar could be set up with platform data.
> 
> Basically, the SD controller or USB host/hub node contains a child that
> represents the socket/port/... that needs some services provided to it
> (power, reset de-asserted, even clocks). The services provided by that
> node are set up before enumeration, so that the device will respond to
> enumeration. Hopefully, the DT representation of this socket/port/..
> could be shared across arbitrary types of controller (so both SD and
> USB) and the driver the "implements" that node would be common code that
> SD and USB call into, rather than having them both re-implement it from
> scratch.

While I think this can be handled generically with SD and USB drivers,
I'm not so sure there would be benefit across them. It is just getting a
gpio and toggling it. But really that's a detail that doesn't matter
until we're closer to an implementation...

Rob