Re: [PATCH] ASoC: fsl_asrc: refine the setting of internal clock divider

[Nicolin Chen]

On Wed, Oct 23, 2019 at 06:25:20AM +0000, S.j. Wang wrote:
> > On Thu, Oct 17, 2019 at 02:21:08PM +0800, Shengjiu Wang wrote:
> > > For P2P output, the output divider should align with the output sample
> > 
> > I think we should avoid "P2P" (or "M2M") keyword in the mainline code as
> > we know M2M will never get merged while somebody working with the
> > mainline and caring about new feature might be confused.
> 
> Ok. But we still curious that is there a way to upstream m2m?

Hmm..I would love to see that happening. Here is an old discussion
that you may want to take a look:
https://mailman.alsa-project.org/pipermail/alsa-devel/2014-May/076797.html

> > It makes sense to me, yet I feel that the delay at the beginning of the audio
> > playback might be longer as a compromise. I am okay with this decision
> > though...
> > 
> > > The maximum divider of asrc clock is 1024, but there is no judgement
> > > for this limitaion in driver, which may cause the divider setting not
> > > correct.
> > >
> > > For non-ideal ratio mode, the clock rate should divide the sample rate
> > > with no remainder, and the quotient should be less than 1024.
> > >
> > > Signed-off-by: Shengjiu Wang <shengjiu.wang@xxxxxxx>

> > > @@ -351,7 +352,9 @@ static int fsl_asrc_config_pair(struct fsl_asrc_pair
> > *pair)
> > >       /* We only have output clock for ideal ratio mode */
> > >       clk = asrc_priv->asrck_clk[clk_index[ideal ? OUT : IN]];
> > >
> > > -     div[IN] = clk_get_rate(clk) / inrate;
> > > +     clk_rate = clk_get_rate(clk);
> > 
> > The fsl_asrc.c file has config.inclk being set to INCLK_NONE and this sets the
> > "ideal" in this function to true. So, although we tend to not use ideal ratio
> > setting for p2p cases, yet the input clock is still not physically connected, so
> > we still use output clock for div[IN] calculation?
> 
> For p2p case, it can be ideal or non-ideal.  For non-ideal, we still use
> Output clock for div calculation.
> 
> > 
> > I am thinking something simplier: if we decided not to use ideal ratio for
> > "P2P", instead of adding "bool p2p" with the confusing "ideal" in this
> > function, could we just set config.inclk to the same clock as the output one
> > for "P2P"? By doing so, "P2P" won't go through ideal ratio mode while still
> > having a clock rate from the output clock for div[IN] calculation here.
> 
> Bool p2p is to force output rate to be sample rate, no impact to ideal
> Ratio mode.

I just realized that the function has a bottom part for ideal mode
exclusively -- if we treat p2p as !ideal, those configurations will
be missing. So you're right, should have an extra boolean variable.

> > 
> > > +     rem[IN] = do_div(clk_rate, inrate);
> > > +     div[IN] = (u32)clk_rate;
> > >       if (div[IN] == 0) {
> > 
> > Could we check div[IN] and rem[IN] here? Like:
> >         if (div[IN] == 0 || div[IN] > 1024) {
> >                 pair_err();
> >                 goto out;
> >         }
> > 
> >         if (!ideal && rem[IN]) {
> >                 pair_err();
> >                 goto out;
> >         }
> > 
> > According to your commit log, I think the max-1024 limitation should be
> > applied to all cases, not confined to "!ideal" cases right? And we should
> > add some comments also, indicating it is limited by hardware.
> 
> For ideal mode,  my test result is  the divider not impact the output result.
> Which means it is ok for ideal mode even divider is not correct... 

OK.

> > 
> > >               pair_err("failed to support input sample rate %dHz by
> > asrck_%x\n",
> > >                               inrate, clk_index[ideal ? OUT : IN]); @@
> > > -360,11 +363,20 @@ static int fsl_asrc_config_pair(struct
> > > fsl_asrc_pair *pair)
> > >
> > >       clk = asrc_priv->asrck_clk[clk_index[OUT]];
> > >
> > > -     /* Use fixed output rate for Ideal Ratio mode (INCLK_NONE) */
> > > -     if (ideal)
> > > -             div[OUT] = clk_get_rate(clk) / IDEAL_RATIO_RATE;
> > > -     else
> > > -             div[OUT] = clk_get_rate(clk) / outrate;
> > > +     /*
> > > +      * When P2P mode, output rate should align with the out samplerate.
> > > +      * if set too high output rate, there will be lots of Overload.
> > > +      * When M2M mode, output rate should also need to align with the
> > > + out
> > 
> > For this "should", do you actually mean "M2M could also"? Sorry, I'm just
> > trying to understand everyting here, not intentionally being picky at words.
> > My understanding is that we still keep the ideal ratio setting because
> > "M2M" still uses it.
> 
> We use IDEAL_RATIO_RATE as output rate for m2m mode, it likes a
> Tricky operation, in order to improve the performance. I think
> The correct operation is to use the real output rate, but the performance
> Is bad.  So it is a compromise.

I see.

> > 
> > > +      * samplerate, but M2M must use less time to achieve good
> > performance.
> > > +      */
> > > +     clk_rate = clk_get_rate(clk);
> > > +     if (p2p || !ideal) {
> > > +             rem[OUT] = do_div(clk_rate, outrate);
> > > +             div[OUT] = clk_rate;
> > > +     } else {
> > > +             rem[OUT] = do_div(clk_rate, IDEAL_RATIO_RATE);
> > > +             div[OUT] = clk_rate;
> > > +     }
> > >
> > >       if (div[OUT] == 0) {
> > >               pair_err("failed to support output sample rate %dHz by
> > > asrck_%x\n", @@ -372,6 +384,16 @@ static int fsl_asrc_config_pair(struct
> > fsl_asrc_pair *pair)
> > >               return -EINVAL;
> > >       }
> > >
> > > +     if (!ideal && (div[IN] > 1024 || div[OUT] > 1024 ||
> > > +                    rem[IN] != 0 || rem[OUT] != 0)) {
> > > +     if (!ideal && (div[IN] > 1024 || div[OUT] > 1024 || rem[IN] ||
> > > + rem[OUT] != 0)) {
> > 
> > So for ideal == true, these limitaions are not applied any more?
> > Remember that the "ideal" is true for "p2p == true" cases here.
> 
> No, not applied.  for ideal, the div don't impact the output result
> Even it is not accurate.

I see.

> > 
> > > +             pair_err("The divider can't be used for non ideal mode\n");
> > > +             return -EINVAL;
> > > +     }
> > > +
> > > +     /* Divider range is [1, 1024] */
> > > +     div[IN] = min_t(u32, 1024, div[IN]);
> > > +     div[OUT] = min_t(u32, 1024, div[OUT]);
> > 
> > Hmm, this looks like we want to allow ideal ratio cases and p2p cases to
> > operate any way, even if the divider wasn't within the range to get the
> > in/out rates from the output clock?
> 
> Yes. We still allow the p2p = true,  ideal = false.  Note that p2p is not
> Equal to ideal.

Got it.

Overall, I feel it's better to have a naming to state the purpose
of using ideal configurations without the IDEAL_RATIO_RATE setup.
	bool use_ideal_rate;
And we can put into the asrc_config structure if there's no major
problem.

So the condition check for the calculation would be:
+	if (ideal && config->use_ideal_rate)
+		rem[OUT] = do_div(clk_rate, IDEAL_RATIO_RATE);
+	else
+		rem[OUT] = do_div(clk_rate, outrate);
+	div[OUT] = clk_rate;

And for that if (!ideal && div[IN]....rem[OUT]), I feel it would
be clear to have them separately, as the existing "div[IN] == 0"
and "div[OUT] == 0" checks, so that we can tell users which side
of the divider is out of range and what the sample rate and clock
rate are.

Thanks
Nicolin