linux-kernel - Re: [alsa-devel] [PATCH] ASoC: SOF: Intel: work around snd_hdac_aligned

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Message-ID: <s5hef0oaav5.wl-tiwai@suse.de>
Date:   Tue, 10 Sep 2019 09:06:38 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        ALSA Development Mailing List <alsa-devel@...a-project.org>,
        Pan Xiuli <xiuli.pan@...ux.intel.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Evan Green <evgreen@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [alsa-devel] [PATCH] ASoC: SOF: Intel: work around snd_hdac_aligned_read link failure

On Mon, 09 Sep 2019 22:51:23 +0200,
Arnd Bergmann wrote:
> 
> On Mon, Sep 9, 2019 at 10:39 PM Pierre-Louis Bossart
> <pierre-louis.bossart@...ux.intel.com> wrote:
> >
> > On 9/9/19 2:51 PM, Arnd Bergmann wrote:
> > > When CONFIG_SND_HDA_ALIGNED_MMIO is selected by another driver
> > > (i.e. Tegra) that selects CONFIG_SND_HDA_CORE as a loadable
> > > module, but SND_SOC_SOF_HDA_COMMON is built-in, we get a
> > > link failure from some functions that access the hda register:
> > >
> > > sound/soc/sof/intel/hda.o: In function `hda_ipc_irq_dump':
> > > hda.c:(.text+0x784): undefined reference to `snd_hdac_aligned_read'
> > > sound/soc/sof/intel/hda-stream.o: In function `hda_dsp_stream_threaded_handler':
> > > hda-stream.c:(.text+0x12e4): undefined reference to `snd_hdac_aligned_read'
> > > hda-stream.c:(.text+0x12f8): undefined reference to `snd_hdac_aligned_write'
> > >
> > > Add an explicit 'select' statement as a workaround. This is
> > > not a great solution, but it's the easiest way I could come
> > > up with.
> >
> > Thanks for spotting this, I don't think anyone on the SOF team looked at
> > this. Maybe we can filter with depends on !TEGRA or
> > !SND_HDA_ALIGNED_MMIO at the SOF Intel top-level instead?
> 
> That doesn't sound much better than my approach, but could also work.
> One idea that I had but did not manage to implement was to move out
> the snd_hdac_aligned_read/write functions from the core hda code
> into a separate file. I think that would be the cleanest solution,
> as it decouples the problem from any drivers.

Yeah, that's a tricky problem because of the reverse-selection, as
usual...

Another solution would be to just avoid byte/word access but use only
long access, i.e. replace snd_hdac_chip_readb() with
snd_hdac_chip_readl() with the aligned register and bit shift.
The aligned access helper is needed only for the register that isn't
aligned with 4 bytes offset.

And, one remaining question is whether it makes sense to enable
CONFIG_SND_SOC_SOF_HDA without CONFIG_SND_HDA_EXT_CORE (that selects
CONFIG_SND_HDA_CORE, too).  Currently it seems conditionally selected,
but many codes do depend on snd_hdac_ext_*() and other helper code
with CONFIG_SND_SOC_SOF_HDA-ifdef.


thanks,

Takashi