linux-kernel - Re: [alsa-devel] [PATCH] ASoC: skl: always select SND_SOC_HDAC

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Date:   Mon, 5 Nov 2018 11:18:07 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Takashi Iwai <tiwai@...e.de>, Arnd Bergmann <arnd@...db.de>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        alsa-devel@...a-project.org,
        Guneshwor Singh <guneshwor.o.singh@...el.com>,
        Naveen Manohar <naveen.m@...el.com>,
        Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@...el.com>,
        Rakesh Ughreja <rakesh.a.ughreja@...el.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        Sriram Periyasamy <sriramx.periyasamy@...el.com>,
        Mark Brown <broonie@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Jie Yang <yang.jie@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [alsa-devel] [PATCH] ASoC: skl: always select SND_SOC_HDAC_HDA


>>> We have this ("strange") lines over the drivers:
>>>
>>> config BAR
>>> depends on FOO || FOO=n
>>>
>>> which guarantees that FOO will be not module when BAR is built-in.
>> That's what I normally use, but I could not figure this one out.
>> One problem is that SND_SOC_ALL_CODECS selects
>> SND_SOC_HDAC_HDA, and SND_SOC_ALL_CODECS itself
>> may be =m, causing the failure for
>> SND_SOC_INTEL_SKL_HDA_DSP_GENERIC_MACH=y.
>>
>> It might work with a separate dummy symbol:
>>
>> config SND_SOC_HDAC_HDA_FORCE
>>           tristate
>>           depends on SND_SOC_ALL_CODECS != n
>>           default SND_SOC_INTEL_SKYLAKE
>>           select SND_SOC_HDAC_HDA
>>
>> This would make SND_SOC_HDAC_HDA built-in even
>> with SND_SOC_ALL_CODECS=m and
>> SND_SOC_INTEL_SKL_HDA_DSP_GENERIC_MACH=n
>>
>> It seems a bit ugly, and would need some testing.
> The mixture of depends and select is often more confusing, so IMO, we
> should align with only select as Pierre's suggestion, in this
> particular case.

I tried to avoid re-adding a "depends on" which we tried to remove last 
year, but there is still a conditional statement which assumes a very 
specific evaluation order.

1. SKYLAKE is enabled as m or y

2. that enables some machine drivers (through an if statement), some of 
which might select HDA audio

3. the selections done within the SKYLAKE config are conditional on the 
outcome of #2.

it seems to work but I don't know if it's by design or an accident :-). 
One could argue it's a hidden "depends on".