linux-kernel - Re: [PATCH 12/19] twl4030: mfd_cell is now implicitly available to drivers

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Message-ID: <20110202230326.167fe873@queued.net>
Date:	Wed, 2 Feb 2011 23:03:26 -0800
From:	Andres Salomon <dilinger@...ued.net>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>, linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Peter Ujfalusi <peter.ujfalusi@...ia.com>,
	Liam Girdwood <lrg@...mlogic.co.uk>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	Timur Tabi <timur@...escale.com>, linux-input@...r.kernel.org,
	alsa-devel@...a-project.org
Subject: Re: [PATCH 12/19] twl4030: mfd_cell is now implicitly available to
 drivers

On Wed, 2 Feb 2011 22:53:39 -0800
Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:

> On Wed, Feb 02, 2011 at 10:39:59PM -0800, Andres Salomon wrote:
> > On Wed, 2 Feb 2011 22:05:21 -0800
> > Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
> > 
> > > On Wed, Feb 02, 2011 at 08:15:22PM -0800, Andres Salomon wrote:
> > > >  static int __devinit twl4030_vibra_probe(struct platform_device
> > > > *pdev) {
> > > > -	struct twl4030_codec_vibra_data *pdata =
> > > > pdev->dev.platform_data;
> > > > +	struct twl4030_codec_vibra_data *pdata =
> > > > platform_get_drvdata(pdev);
> > > 
> > > No, device's drvdata belongs to _this_ driver, and it is supposed
> > > to manage it and use as it sees fit.
> > 
> > Right, so it's used to pass data to the probe function; once the
> > probe function has obtained the pdata pointer, it's free to do with
> > it what it will.
> > 
> > 
> > > 
> > > Note platform_set_drvdata(pdev, info) later in this function along
> > > with platform_set_drvdata(pdev, NULL) in twl4030_vibra_remove(),
> > > which means that with your change you will be able to bind the
> > > device only once.
> > > 
> > 
> > Hm, good point; if the driver is reloaded, the pdev that was
> > created by mfd-core will have lost the pointer to pdata.
> > 
> > I wonder if I should be using mfd's driver_data instead. I used
> > platform_data because a bunch of drivers had already made use of it
> > to pass cell information..
> 
> Then they are doing it incorrectly. One possible way is to have parent
> device carry relevant data in its drvdata and have children get it
> from there.
> 

I believe some drivers are even using the parent device already.  See
drivers/leds/leds-mc13783.c, for example, whose parent device drvdata
is used to pass around a struct mc13783 to its children.  Sounds
like a possibility, will need to look into it further.


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