linux-kernel - Re: [RFC PATCH 2/7] ALSA: ac97: add an ac97 bus

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Message-ID: <87mvnrhux4.fsf@belgarion.home>
Date:	Sun, 15 May 2016 23:29:27 +0200
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	"Haojian Zhuang" <haojian.zhuang@...il.com>,
	"Liam Girdwood" <lgirdwood@...il.com>,
	"Mark Brown" <broonie@...nel.org>,
	"Jaroslav Kysela" <perex@...ex.cz>,
	"Daniel Mack" <daniel@...que.org>, <alsa-devel@...a-project.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<patches@...nsource.wolfsonmicro.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 2/7] ALSA: ac97: add an ac97 bus

Takashi Iwai <tiwai@...e.de> writes:

> On Sat, 14 May 2016 11:50:50 +0200,
> Robert Jarzmik wrote:
>> >> +unsigned int ac97_bus_scan_one(struct ac97_controller *ac97,
>> >> +				      int codec_num)
>> >> +{
>> >> +	struct ac97_codec_device codec;
>> >> +	unsigned short vid1, vid2;
>> >> +	int ret;
>> >> +
>> >> +	codec.dev = *ac97->dev;
>> >> +	codec.num = codec_num;
>> >> +	ret = ac97->ops->read(&codec, AC97_VENDOR_ID1);
>> >> +	vid1 = (ret & 0xffff);
>> >> +	if (ret < 0)
>> >> +		return 0;
>> >
>> > Hmm.  This looks pretty hackish and dangerous.
>> You mean returning 0 even if the read failed, right ?
>
> No, my concern is that it's creating a dummy codec object temporarily
> on the stack just by copying some fields and calling the ops with it.
> (And actually the current code may work wrongly because lack of
>  zero-clear of the object.)
Ah yes, I remember now, the on-stack generated device, indeed ugly.

> IMO, a cleaner way would be to define the ops passed with both
> controller and codec objects as arguments, and pass NULL codec here.
It's rather unusual to need both the device and its controller in bus
operations. I must admit I have no better idea so far, so I'll try that just to
see how it looks like, and let's see next ...

Cheers.

-- 
Robert