On Thu, Jan 14, 2016 at 08:29:42AM -0800, Caleb Crome wrote: > Tuning the SSI fifo watermark & maxburst settings needs to be > optimized differently depending on the demands on the system. The > current default of 2 is too low for high data-rate systems. This > patch maintains exactly the same behavior by default (i.e defaults to > 2), but adds device tree options to set maxburst & fifo depth from the > device tree. This is necessary because a setting of 2 simply doesn't > work at higher data rates. > @@ -61,6 +61,16 @@ Optional properties: > - fsl,mode: The operating mode for the AC97 interface only. > "ac97-slave" - AC97 mode, SSI is clock slave > "ac97-master" - AC97 mode, SSI is clock master > +- fsl,fifo-watermark: Sets the fifo watermark. The default is > + fifo_depth-2 words, meaning 'initiate dma transfer > + when 2 words are left in the fifo'. At higher > + data rates (48kHz, 16-channels for example), this > + causes silent but deadly DMA xruns and channel > + slips. For 15 word FIFOs (like on MX5, MX6) 8 is > + a good value when running at high data rates > +- fsl,dma-maxburst: sets the max number of words to transfer in DMA. > + This defaults to the same value as > + fsl,fifo-watermark. I think DT maintainers may not give a consent towards these two properties as they are not to describe the hardware but to hack software configurations. (And it seems you haven't CCed them.) I forgot which values you've figured out for these two properties, but I think those two values should work for normal cases as well: as SSI only has limited FIFO depth, it won't hurt (increasing too much latency) even if using a higher watermark configuration imo. So it could be a good idea to use optimized settings for all use cases and let other users test it. Nicolin -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
