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

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Message-ID: <20191025065433.GA4632@Asurada>
Date:   Thu, 24 Oct 2019 23:54:34 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     "S.j. Wang" <shengjiu.wang@....com>
Cc:     "timur@...nel.org" <timur@...nel.org>,
        "Xiubo.Lee@...il.com" <Xiubo.Lee@...il.com>,
        "festevam@...il.com" <festevam@...il.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "perex@...ex.cz" <perex@...ex.cz>,
        "tiwai@...e.com" <tiwai@...e.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: fsl_asrc: refine the setting of internal clock
 divider

On Fri, Oct 25, 2019 at 05:33:17AM +0000, S.j. Wang wrote:
> > > > > +             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.
> > 
> 
> Asrc_config may exposed to user, I don't think user need to care about
> The using of ideal rate or not. 

Given that M2M could use output rate instead of ideal ratio rate
as well, it could be a configuration from my point of view. Yet,
we may just add it as a function parameter like you did, for now
to ease the situation, until we have such a need someday.

> 
> > 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.
> > 
> Do you mean need to combine this judgement with "div[IN] == 0"
> Or "div[OUT] == 0"?

Not necessarily. Could put in the else path so its error message
would be more ideal ratio configuration specific.

Thanks