linux-kernel - Re: [PATCH] cw1200: fix some obvious mistakes

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Message-ID: <20130605040802.GA22735@shaftnet.org>
Date:	Wed, 5 Jun 2013 00:08:02 -0400
From:	Solomon Peachy <pizza@...ftnet.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-kernel@...r.kernel.org,
	"John W. Linville" <linville@...driver.com>,
	Wei Yongjun <yongjun_wei@...ndmicro.com.cn>,
	Dmitry Tarnyagin <dmitry.tarnyagin@...kless.no>,
	Ajitpal Singh <ajitpal.singh@...ricsson.com>,
	linux-wireless@...r.kernel.org
Subject: Re: [PATCH] cw1200: fix some obvious mistakes

On Mon, Jun 03, 2013 at 10:40:42AM +0200, Arnd Bergmann wrote:
> It's much better than what you have today, but not ideal because it
> means the driver cannot be a loadable module any more.

At least not when being built with platform data, anyway.

I suppose the next step here is to define some devicetree mappings for 
this device.

> At least it's not in a released kernel yet.

Given the boneheaded buffer overflow bug that was just pointed out (and 
fixed), I'm glad it's getting a lot more scrutiny.

> Regarding a long-term solution, I think what we should do here is to
> move the reset logic into the SDIO framework itself: We have similar
> requirements even for eMMC and SD cards, where you need to provide
> the correct voltage to a device on the MMC port in order for it to
> work. Today this is supported to a varying degree on the MMC controller
> level, where we hook into various frameworks (clk, reset-controller,
> regulator, gpio, pinctrl, power domain) based on platformm data or
> device tree information on the controller node.

If I understand you correctly, the "traditional" platform data -- power 
supply, clock source, and gpio (ie POWERUP, RESET) lines would be 
brought up using this mechanism, in order to get the device to attach to 
the SDIO bus.  One wrinkle here is that the cw1200 has some minimum 
timing requirements between when each of those signals are brought up; I 
don't know if there's a way to encode that into the devicetree.

But that's only half the equation.

Once the device has identified it to the SDIO bus and the driver's 
probe() function is called, the other half of the platform data is 
needed to successfully probe the hardware.  Namely, the 'ref_clk' field. 
This would need to be made available to the probe() call (eg via 
func->dev.platform_data) but from what I can tell there's currently no 
mechanism to make that connection.

Anyway, it's time for bed.

 - Solomon
-- 
Solomon Peachy        		       pizza at shaftnet dot org	 
Delray Beach, FL                          ^^ (email/xmpp) ^^
Quidquid latine dictum sit, altum viditur.

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