From: grant.likely@secretlab.ca (Grant Likely)
To: linux-arm-kernel@lists.infradead.org
Subject: [RFC/PATCH 7/7] WIP: HACK/RFC: omap_device: begin to decouple platform_device from omap_device
Date: Mon, 1 Aug 2011 16:44:20 +0100 [thread overview]
Message-ID: <CACxGe6t4tNeD-Pn6WFt1XOMC=_Q0cf4uD3kRkOckKH+S1JUJDA@mail.gmail.com> (raw)
In-Reply-To: <871ux5nnop.fsf@ti.com>
On Mon, Aug 1, 2011 at 4:42 PM, Kevin Hilman <khilman@ti.com> wrote:
> Russell King - ARM Linux <linux@arm.linux.org.uk> writes:
>
>> On Sat, Jul 30, 2011 at 08:58:07PM -0600, Grant Likely wrote:
>>> On Sat, Jul 30, 2011 at 01:03:32PM +0100, Russell King - ARM Linux wrote:
>>> > On Thu, Jul 21, 2011 at 04:52:18PM -0700, Kevin Hilman wrote:
>>> > > Rather than embedding a struct platform_device inside a struct
>>> > > omap_device, decouple them, leaving only a pointer to the
>>> > > platform_device inside the omap_device.
>>> > >
>>> > > This patch uses devres to allocate and attach the omap_device to the
>>> > > struct device, so finding an omap_device from a struct device means
>>> > > using devres_find(), and the to_omap_device() helper function was
>>> > > modified accordingly.
>>> > >
>>> > > RFC/Hack alert:
>>> > >
>>> > > Currently the driver core (drivers/base/dd.c) doesn't expect any
>>> > > devres resources to exist before the driver's ->probe() is called. ?In
>>> > > this patch, I just comment out the warning, but we'll need to
>>> > > understand why that limitation exists, and if it's a real limitation.
>>> > > A first glance suggests that it's not really needed. ?If this is a
>>> > > true limitation, we'll need to find some way other than devres to
>>> > > attach an omap_device to a struct device.
>>> > >
>>> > > On OMAP, we will need an omap_device attached to a struct device
>>> > > before probe because device HW may be disabled in probe and drivers
>>> > > are expected to use runtime PM in ->probe() to activate the hardware
>>> > > before access. ?Because the runtime PM API calls use omap_device (via
>>> > > our PM domain layer), we need omap_device attached to a
>>> > > platform_device before probe.
>>> >
>>> > This feels really wrong to overload devres with this. ?devres purpose is
>>> > to provide the device's _drivers_ with a way to allocate and free resources
>>> > in such a way to avoid leaks on .remove or probe failure. ?So I think that
>>> > overloading it with something that has a different lifetime is completely
>>> > wrong.
>>>
>>> I disagree; extending devres to also handle device lifetime scoped
>>> resources makes perfect sense. It is a clean extension, and struct device
>>> is really getting rather huge. ?I certainly prefer re-scoping devres
>>> to adding more elements to struct device.
>>
>> The point is you're asking something which is designed to have a well
>> defined lifetime of driver-bind...driver-unbind to do a lot more than
>> that - extending its lifetime conditional on some flag to the entire
>> device lifetime instead.
>>
>> Such extensions tend to be a disaster - and a recipe for confusion as
>> people will no longer have a clear idea of the lifetime issues. ?We
>> already know that people absolutely struggle to understand lifed
>> objects - we see it time and time again where people directly kfree
>> stuff like platform devices without thinking about whether they're
>> still in use.
>>
>> So no, extending devres is a _big_ mistake and is far from clean.
>>
>> Not only that, but if most of the platform devices are omap devices,
>> (as it would be on OMAP), you'll consume more memory through having to
>> have the additional management structs for the omap_device stuff than
>> a simple pointer.
>>
>> As for struct device getting rather huge, last time I looked it contained
>> a load of stuff which was there whether or not a platform used it. ?Eg,
>> you get 4 bytes wasted for an of_node whether you have DT support or not.
>> If sizeof(struct device) really is a problem, then it needs the unused
>> stuff ifdef'd away. ?So I don't buy the "its getting rather huge" argument.
>>
>>> > We could add a new member to struct dev_archdata or pdev_archdata to carry
>>> > a pointer to this data, which I think would be a far cleaner (and saner)
>>> > way to deal with this. ?In much the same way as we already have an of_node
>>> > member in struct device.
>>>
>>> Since this is just for omap_device, which by definition is arm-only, I
>>> don't have any strong objection to using pdev_archdata. If it was
>>> cross-architecture, then I'd argue strongly for the devres approach.
>>
>> Indeed, which is why I think putting it in the platform device archdata
>> makes total sense, more sense than buggering up the clean devres lifetime
>> rules that we have today.
>
> OK, so I'll continue this approach using pdev_archdata, which would work
> fine for me. ?It's currently empty, so I'll just add a 'void *' if it's
> OK with you Russell:
>
> diff --git a/arch/arm/include/asm/device.h b/arch/arm/include/asm/device.h
> index 9f390ce..bb777cd 100644
> --- a/arch/arm/include/asm/device.h
> +++ b/arch/arm/include/asm/device.h
> @@ -13,6 +13,7 @@ struct dev_archdata {
> ?};
>
> ?struct pdev_archdata {
> + ? ? ? void *p;
> ?};
struct omap_device *p;
Otherwise it is just asking for type safety problems.
g.
next prev parent reply other threads:[~2011-08-01 15:44 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-21 23:52 [RFC/PATCH 0/7] decouple platform_device from omap_device Kevin Hilman
2011-07-21 23:52 ` [PATCH] OMAP: omap_device: replace _find_by_pdev() with to_omap_device() Kevin Hilman
2011-07-22 8:53 ` Felipe Balbi
2011-07-21 23:52 ` [RFC/PATCH 1/7] OMAP: omap_device: replace debug/warning/error prints with dev_* macros Kevin Hilman
2011-07-21 23:52 ` [RFC/PATCH 2/7] OMAP3: beagle: don't touch omap_device internals Kevin Hilman
2011-07-22 8:57 ` Felipe Balbi
2011-07-28 5:53 ` Nishanth Menon
2011-07-28 10:10 ` Russell King - ARM Linux
2011-07-28 12:57 ` Cousson, Benoit
2011-07-28 12:59 ` Felipe Balbi
2011-07-28 13:31 ` Menon, Nishanth
2011-07-29 13:49 ` Nishanth Menon
2011-07-29 14:05 ` Felipe Balbi
2011-07-29 23:07 ` Menon, Nishanth
2011-08-01 8:52 ` Felipe Balbi
2011-07-28 8:36 ` Jean Pihet
2011-07-28 8:40 ` Jean Pihet
2011-07-21 23:52 ` [RFC/PATCH 3/7] OMAP: McBSP: use existing macros for converting between devices Kevin Hilman
2011-07-22 8:58 ` Felipe Balbi
2011-07-22 12:32 ` Sergei Shtylyov
2011-07-22 20:19 ` Kevin Hilman
2011-07-21 23:52 ` [RFC/PATCH 4/7] OMAP: omap_device: remove internal functions from omap_device.h Kevin Hilman
2011-07-21 23:52 ` [RFC/PATCH 5/7] OMAP: omap_device: when building return platform_device instead of omap_device Kevin Hilman
2011-07-21 23:52 ` [RFC/PATCH 6/7] OMAP: omap_device: device register functions now take platform_device pointer Kevin Hilman
2011-07-22 6:16 ` Grant Likely
2011-07-21 23:52 ` [RFC/PATCH 7/7] WIP: HACK/RFC: omap_device: begin to decouple platform_device from omap_device Kevin Hilman
2011-07-22 2:20 ` Grant Likely
2011-07-30 12:03 ` Russell King - ARM Linux
2011-07-31 2:58 ` Grant Likely
2011-07-31 15:05 ` Russell King - ARM Linux
2011-08-01 15:42 ` Kevin Hilman
2011-08-01 15:44 ` Grant Likely [this message]
2011-08-01 18:50 ` Felipe Balbi
2011-08-01 20:07 ` Russell King - ARM Linux
2011-08-01 22:11 ` Kevin Hilman
2011-08-01 22:55 ` Felipe Balbi
2011-08-01 23:09 ` Russell King - ARM Linux
2011-08-02 0:00 ` Grant Likely
2011-07-27 14:04 ` [RFC/PATCH 0/7] " G, Manjunath Kondaiah
2011-07-27 21:45 ` Hilman, Kevin
2011-07-28 4:50 ` G, Manjunath Kondaiah
2011-07-29 23:59 ` Kevin Hilman
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