Hi, On Tue, Aug 2, 2016 at 11:05 PM, Thomas Niederprüm <niederp@xxxxxxxxxxxxxxxx> wrote: > I am using the new sun4i-i2s driver in linux-next to run a sta326 codec > via the pin header on a cubietruck (this involves some soldering as > described in [1]). The codec can only be configured as slave and needs > a master clock for its internal PLL. It is therefore great that, unlike > many other SOCs, the a20 provides a MCLK that can be used to sync the > codec. However, in my case there is a restriction imposed on the MCLK > by the codec. As stated in the datasheet [2], the master clock should > be at maximum 12.288 MHz/11.2896 MHz or otherwise the codec will not > work (confirmed by experiment!). > > Since the mod clock of the a20's dai block is running at twice this > frequency, I need to assure that the MLCK divider is at least 2. > Actually it is rather straight forward to achieve this by changing the > breaking condition in the divider calculation, as shown by the > following one-line patch: > > diff --git a/sound/soc/sunxi/sun4i-i2s.c b/sound/soc/sunxi/sun4i-i2s.c > index 687a8f8..8920844 100644 > --- a/sound/soc/sunxi/sun4i-i2s.c > +++ b/sound/soc/sunxi/sun4i-i2s.c > @@ -206,7 +206,7 @@ static int sun4i_i2s_set_clk_rate(struct sun4i_i2s > *i2s, > clk_rate, > rate); > > - if ((bclk_div >= 0) && (mclk_div >= 0)) > + if ((bclk_div >= 0) && (mclk_div >= 1)) > break; > } > > Of course, this is just a hack to fix my use case and I am wondering > what would be the best way to handle my corner case more generally? I > see one option in introducing a DT property mlck_mindiv, or similar, > that defaults to 1 and can be overwritten at the board level. I'm > willing to prepare a proper patch to tackle this problem but right now > I'm wondering if there a major objections to this approach or whether > there is any better solution to the problem. I think the proper way would be to have sun4i-i2s support the .set_sysclk callback in .dai_ops. simple-card calls snd_soc_dai_set_sysclk if you have the "mclk-fs" property set in the DT. Regards ChenYu > > Best regards, > > Thomas > > [1] https://hifiduino.wordpress.com/2014/03/07/cubieboard-for-audio/ > [2] www.st.com/resource/en/datasheet/sta326.pdf > _______________________________________________ > Alsa-devel mailing list > Alsa-devel@xxxxxxxxxxxxxxxx > http://mailman.alsa-project.org/mailman/listinfo/alsa-devel _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
