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

On Wed, Jun 27, 2012 at 05:26:04AM +0800, Rob Herring wrote:

On 06/26/2012 11:53 AM, Stephen Warren wrote:

quoted

(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:

quoted

On Tue, Jun 19, 2012 at 06:01:54PM -0600, Stephen Warren wrote:

...

quoted

quoted

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@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@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@78000000 {
	compatible = "nvidia,tegra30-sdhci", "nvidia,tegra20-sdhci";
	reg = <0x78000000 0x200>;
	interrupts = <0 14 0x04>;

	sdio-device-option@0 {
		compatible = "broadcom,bcm4239";
		reset-gpios = <...>;
		enable-gpios = <...>;
	};

	sdio-device-option@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

quoted

sdhci@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.

Those properties are sdio-device specific, the host may be hard to
know to handle it in a common way.

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

Yes, may need special timing.

Regards
Dong Aisheng