[alsa-devel] [PATCH] ASoC: rcar: revert IOMMU support so far

[Kuninori Morimoto]

Hi Takashi-san

> > > The driver may return the position at the last synced point via
> > > pointer callback while keeping the finer position by compensating with
> > > status delay field.  In that way, user-space can avoid to touch the
> > > in-flight memory but can know the exact position.
> > > 
> > > BTW, if the problem is only about PA, the easiest workaround would be
> > > to put SNDRV_PCM_INFO_BATCH flag.  Then PA switches from tsched to
> > > normal mode.
> > 
> > The issue (= noise) is not only for PulseAudio, but
> > NormalAudio had capture noise issue.
> 
> OK, it indicates that returning the value with residue is actually
> wrong.  Basically the pointer callback needs to give the position that
> has been already processed where you can safely scratch at this point
> at most.
> 
> > Maybe we can use "delay" field, but this IOMMU patch is assuming
> > many things which is no guarantee anyway, I can say dirty.
> > And Renesas platform is not yet enabled IOMMU at this point.
> > Thus, removing IOMMU support has no degrade, and will be fresh.
> > 
> > IOMMU support on this driver was created based on local prototype
> > SoC IOMMU support.
> > So, I want to fresh create new IOMMU support in the future
> 
> Sure, I'm not against the revert, which is the safest option, but just
> wanted to mention about a right implementation in such scenarios.

Thank you for your help/advice.

Best regards
---
Kuninori Morimoto