Re: twl4030_charger: need changes to get probed?

From: NeilBrown <neilb@suse.de>
To: Sebastian Reichel <sre@debian.org>
Cc: Pavel Machek <pavel@ucw.cz>,
	pali.rohar@gmail.com, kernel list <linux-kernel@vger.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-omap@vger.kernel.org, tony@atomide.com, khilman@kernel.org,
	aaro.koskinen@iki.fi, ivo.g.dimitrov.75@gmail.com,
	patrikbachan@gmail.com, Samuel Ortiz <sameo@linux.intel.com>,
	Lee Jones <lee.jones@linaro.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>,
	David Woodhouse <dwmw2@infradead.org>,
	GTA04 owners <gta04-owner@goldelico.com>,
	linux-pm@vger.kernel.org
Subject: Re: twl4030_charger: need changes to get probed?
Date: Mon, 9 Mar 2015 11:06:53 +1100	[thread overview]
Message-ID: <20150309110653.7532613c@notabene.brown> (raw)
In-Reply-To: <20150307210102.GL5233@earth>

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On Sat, 7 Mar 2015 22:01:02 +0100 Sebastian Reichel <sre@debian.org> wrote:

> Hi,
> 
> On Fri, Mar 06, 2015 at 10:24:17PM +0100, Pavel Machek wrote:
> > According to n900 dts, twl4030-bci (aka charger) should be
> > included.
> 
> its part of twl, but not used on N900 afaik.
> 
> > (But it does not seem to do anything useful on n900. I was hoping for
> > measurement of input voltage, but .. no.)
> 
> check for rx51-battery.
> 
> > Any ideas why the patch below is needed?
> 
> platform_driver_probe() does not support deferred probing.
> 
> Neil, can you take this patch into your series for the next round?

I could, but I do wonder if it is the right thing to do.

Shouldn't we fix platform_driver_probe() to support deferred probing.

As I understand it, it refused to retry a probe if there is an error, and the
comments suggest that such retrying is avoided because it would be a waste
of time:

	/*
	 * Prevent driver from requesting probe deferral to avoid further
	 * futile probe attempts.
	 */

In this case, it isn't futile.

Earlier there is a comment saying:

 * Use this instead of platform_driver_register() when you know the device
 * is not hotpluggable and has already been registered, and you want to
 * remove its run-once probe() infrastructure from memory after the driver
 * has bound to the device.

I presume all this applies.  I assume that the only problem is a probe-order
thing.  So maybe we should fix platform_driver_probe() to do the right thing
with -EPROBEDEFER??

Trouble is, I really don't understand the  point or mechanism for
platform_driver_probe(), so I cannot suggest anything.
But I have been annoyed before that platform_driver_probe doesn't cope with
EPROBEDEFER, so I would like it fixed.

NeilBrown

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