linux-kernel - Re: [RFC] pwm: chip_data vs device

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Message-ID: <20151006091434.GC22087@ulmo.nvidia.com>
Date:	Tue, 6 Oct 2015 11:14:34 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Olliver Schinagl <oliver+list@...inagl.nl>
Cc:	linux-pwm@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Olliver Schinagl <oliver@...inagl.nl>
Subject: Re: [RFC] pwm: chip_data vs device_data

On Tue, Oct 06, 2015 at 10:21:34AM +0200, Olliver Schinagl wrote:
> Hey Thierry,
> 
> thans for your quick reply :)
> 
> On 06-10-15 09:38, Thierry Reding wrote:
> >On Tue, Oct 06, 2015 at 09:20:53AM +0200, Olliver Schinagl wrote:
> >>Hey Thierry, list,
> >>
> >>While working on something in the pwm framework, I noticed that the void
> >>*data in the pwm_device struct is called chip_data. Why is it not called
> >>device_data, since it is the data associated with a PWM device, rather then
> >>the chip, and on that note, if it really is chip related data (thus covering
> >>the whole chip, not just the single pwm device) why is there no chip_data in
> >>pwm_chip?
> >The reason for the name is that it's chip-specific data associated with
> >a struct pwm_device. That is, a PWM chip implementation (i.e. driver)
> >can use it to keep per-PWM data that's not in struct pwm_device itself.
> Then I have to wrap my head around what is a chip and what is a device :)
> 
> To me, it seems that a chip can hold X number of pwm devices, and each
> pwm_device has a unique set of properties, duty, plarity, period. So it
> seems that some device specific data could go here as well, where i'm bad at
> examples now

I think we're really talking about the same thing here. This is used for
device-specific data. The chip_ prefix merely means that the chip driver
"owns" the data.

> >>Again, is this something worth my time to add a device_data and rename
> >>chip_data?
> >device_data would be redundant because it's already part of struct
> >pwm_device. Plain data might be okay, but I like the chip_ prefix
> >because it marks the data as being chip-specific data rather than
> >generic.
> well here i'd imagine the chip specific data (not allready in the struct).

Data specific to a chip is what you're supposed to embed in your driver-
specific data structure (which embeds struct pwm_chip). Like you said it
is data that pertains to the whole chip, so doesn't need to be per-PWM.

Thierry

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