Re: [PATCH v2 3/7] ASoC: fsl_sai: Add support to enable multiple data lines

[Nicolin Chen <nicoleotsuka@gmail.com>]

On Tue, Aug 06, 2019 at 06:23:27PM +0300, Daniel Baluta wrote:
> On Mon, Jul 29, 2019 at 11:22 PM Nicolin Chen <nicoleotsuka@gmail.com> wrote:
> >
> > On Sun, Jul 28, 2019 at 10:24:25PM +0300, Daniel Baluta wrote:
> > > SAI supports up to 8 Rx/Tx data lines which can be enabled
> > > using TCE/RCE bits of TCR3/RCR3 registers.
> > >
> > > Data lines to be enabled are read from DT fsl,dl-mask property.
> > > By default (if no DT entry is provided) only data line 0 is enabled.
> > >
> > > Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
> > > ---
> > >  sound/soc/fsl/fsl_sai.c | 11 ++++++++++-
> > >  sound/soc/fsl/fsl_sai.h |  4 +++-
> > >  2 files changed, 13 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/sound/soc/fsl/fsl_sai.c b/sound/soc/fsl/fsl_sai.c
> > > index 637b1d12a575..5e7cb7fd29f5 100644
> > > --- a/sound/soc/fsl/fsl_sai.c
> > > +++ b/sound/soc/fsl/fsl_sai.c
> > > @@ -601,7 +601,7 @@ static int fsl_sai_startup(struct snd_pcm_substream *substream,
> > >
> > >       regmap_update_bits(sai->regmap, FSL_SAI_xCR3(tx),
> > >                          FSL_SAI_CR3_TRCE_MASK,
> > > -                        FSL_SAI_CR3_TRCE);
> > > +                        FSL_SAI_CR3_TRCE(sai->soc_data->dl_mask[tx]);
> > >
> > >       ret = snd_pcm_hw_constraint_list(substream->runtime, 0,
> > >                       SNDRV_PCM_HW_PARAM_RATE, &fsl_sai_rate_constraints);
> > > @@ -888,6 +888,15 @@ static int fsl_sai_probe(struct platform_device *pdev)
> > >               }
> > >       }
> > >
> > > +     /*
> > > +      * active data lines mask for TX/RX, defaults to 1 (only the first
> > > +      * data line is enabled
> > > +      */
> > > +     sai->dl_mask[RX] = 1;
> > > +     sai->dl_mask[TX] = 1;
> > > +     of_property_read_u32_index(np, "fsl,dl-mask", RX, &sai->dl_mask[RX]);
> > > +     of_property_read_u32_index(np, "fsl,dl-mask", TX, &sai->dl_mask[TX]);
> >
> > Just curious what if we enable 8 data lines through DT bindings
> > while an audio file only has 1 or 2 channels. Will TRCE bits be
> > okay to stay with 8 data channels configurations? Btw, how does
> > DMA work for the data registers? ESAI has one entry at a fixed
> > address for all data channels while SAI seems to have different
> > data registers.
> 
> Hi Nicolin,
> 
> I have sent v3 and removed this patch from the series because we
> need to find a better solution.

Ack. I was in that private mail thread. So it's totally fine.

> 
> I think we should enable TCE based on the number of available datalines
> and the number of active channels.  Will come with a RFC patch later.

Yea, that's exactly what I suspected during patch review and
what I suggested previously too. Look forward to your patch.

> Pasting here the reply of SAI Audio IP owner regarding to your question above,
> just for anyone to have more info of our private discussion:
> 
> If all 8 datalines are enabled using TCE then the transmit FIFO for
> all 8 datalines need to be serviced, otherwise a FIFO underrun will be
> generated.
> Each dataline has a separate transmit FIFO with a separate register to
> service the FIFO, so each dataline can be serviced separately. Note
> that configuring FCOMB=2 would make it look like ESAI with a common
> address for all FIFOs.
> When performing DMA transfers to multiple datalines, there are a
> couple of options:
>     * Use 1 DMA channel to copy first slot for each dataline to each
> FIFO and then update the destination address back to the first
> register.
>     * Configure separate DMA channel for each dataline and trigger the
> first one by the DMA request and the subsequent channels by DMA
> linking or scatter/gather.
>     * Configure FCOMB=2 and treat it the same as the ESAI. This is
> almost the same as 1, but don’t need to update the destination
> address.
> 
> Thanks,
> Daniel.