linux-kernel - Re: [alsa-devel] [RFC PATCH] ASoC: Modify check condition of multiple bindings of components

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Date:	Tue, 13 Oct 2015 16:42:11 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Koro Chen <koro.chen@...iatek.com>
CC:	broonie@...nel.org, perex@...ex.cz, tiwai@...e.de,
	lgirdwood@...il.com, alsa-devel@...a-project.org,
	srv_heupstream@...iatek.com, s.hauer@...gutronix.de,
	linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
	p.zabel@...gutronix.de, linux-arm-kernel@...ts.infradead.org
Subject: Re: [alsa-devel] [RFC PATCH] ASoC: Modify check condition of multiple
 bindings of components

On 10/13/2015 04:18 PM, Koro Chen wrote:
> On Tue, 2015-10-13 at 15:44 +0200, Lars-Peter Clausen wrote:
>> On 10/13/2015 03:37 PM, Koro Chen wrote:
>>> The patch "ASoC: Prevent components from being bound to multiple cards"
>>> adds check to prevent multiple cards from using the same component.
>>> However, snd_soc_register_platform() or snd_soc_register_codec() will
>>> also create components, and sharing the same platform by multiple cards
>>> is then refused. This happens with a platform having multiple
>>> independent DAIs that share the same DMA controller.
>>>
>>> Relax the condition by checking component->registered_as_component,
>>> which is only true in case of snd_soc_register_component() and
>>> will be false for components created by snd_soc_register_platform()
>>> or snd_soc_register_codec().
>>
>> Binding a component to multiple cards results in internal data structure
>> corruption, regardless of whether it is a raw component, CODEC or platform,
>> which is why the check was added. So the proposed change wont work.
>>
> Thanks for your comment. Is it possible to share an example of how the
> data structure will be corrupted? So I can study into this further.

Just look at soc_probe_component() and think about what happens if that runs
twice for two different cards. Multiple calls to list_add() on the same
list, controls are added multiple times, DAPM widgets are created multiple
times, the card field will only point to the last card.

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