linux-kernel - Re: [PATCH RFC 3/3] drm/exynos: use pending

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Message-id: <53562BA4.6020902@samsung.com>
Date:	Tue, 22 Apr 2014 10:43:16 +0200
From:	Andrzej Hajda <a.hajda@...sung.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	dri-devel@...ts.freedesktop.org,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Inki Dae <inki.dae@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	"moderated list:ARM/S5P EXYNOS AR..." 
	<linux-samsung-soc@...r.kernel.org>,
	Tomasz Figa <t.figa@...sung.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	David Airlie <airlied@...ux.ie>,
	open list <linux-kernel@...r.kernel.org>,
	"moderated list:ARM/S5P EXYNOS AR..." 
	<linux-arm-kernel@...ts.infradead.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH RFC 3/3] drm/exynos: use pending_components for	components
 tracking

Hi Russel,

My answer little bit later due to Easter.

On 04/18/2014 02:42 PM, Russell King - ARM Linux wrote:
> On Fri, Apr 18, 2014 at 01:27:53PM +0200, Andrzej Hajda wrote:
>> Hi Russel,
>>
>> Thanks for comments.
>>
>> On 04/17/2014 11:47 PM, Russell King - ARM Linux wrote:
>>> On Thu, Apr 17, 2014 at 01:28:50PM +0200, Andrzej Hajda wrote:
>>>> +out:
>>>> +	if (ret != -EPROBE_DEFER)
>>>> +		exynos_drm_dev_ready(&pdev->dev);
>>> So we end up with everyone needing a "ready" call in each sub-driver
>>> back into the main driver... this makes it impossible to write a
>>> generic subcomponent driver which is not tied in any way to the
>>> main driver.
>>>
>>> That is quite some restriction, and would prevent, for example, the
>>> TDA998x driver being used both with Armada DRM, tilcdc and any other
>>> driver.
>> As I see in armada driver drm is deferred in case tda998x is not yet
>> available. The same solution can be still used with pending_devices
>> approach - the main driver will not report its readiness until tda998x
>> is present.
>>
>> Anyway it still seems to be better than componentize every driver which can
>> probably become a part of some superdevice.
>>
>> If you want to get rid of deferred probe one can make global list of
>> 'ready' devices with notifications systems for master devices.
>>
>> Maybe it would be good to consider notification system for devices probe
>> result,
>> it will require that driver register all its interfaces in probe, ie its
>> readiness cannot
>> be reported later but will not require to add new framework. I hope just
>> extending current
>> notification system should be enough.
> You aren't addressing my point.  If I were to convert tda998x to use
> your infrastructure, then I would have to add in ifdefs to tie it into
> armada DRM _and_ a different set of ifdefs to tie it into tilcdc.  Then
> when someone else wanted to use it in their driver, they'd have to add
> yet more ifdefs into it to tie it into their driver.
>
> This does not scale.

As I already answered, you should not use 'my' framework for tda998x
driver, you can still use current approach with deferred probe. I am not
sure
why have you used ifdefs in armada, tilcdc also uses tda998x and without
ifdefs.

'My' framework (I think helper library is a better name) was created to
use with
devices which are closely tied together by another framework - case
of some SoC devices.


>
> So, please address my point: in your system, how can a single component
> be shared between multiple different master drivers?
>

I have answered this question above, again. But your question suggests
you want to componentize
also drivers which are shared by different DRMs. How do you want to do it?
- componentize all DRM drivers sharing given driver?
- componentize shared device in a way that it can used by
non-componentized devices? how? I guess it
will be possible but will have some price.

Regards
Andrzej



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