On Fri, Jun 14, 2013 at 11:41:10AM +0400, Alexander Shiyan wrote: > Hello. > > Analysis of driver imx-drm led me to believe that the use fractional part of > the divider is not always a good idea. > For example, for a parallel display bus connected to LVDS converter chip > (DS90C363), in this case the use of > fractional part, clock will unstable and the on-chip PLL is not working > properly, or rather, does not work at all. > > Let me give a specific example. > ipu_crtc_mode_set 0x36314752 > imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000035 > outrate: 40150928 wanted: 40000000 > imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000035 > outrate: 40150928 wanted: 40150928 > imx-ipuv3 40000000.ipu: clk_di_set_rate: inrate: 133000000 desired: 40150928 > div: 0x00000035 > > In this case the divider is 3.5, that result to clock is incorrect. See an > attached oscillogram F0000TEK.jpg. > > After a patch the clocks is OK. Patch just uncomment some FSL code. > imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000040 > outrate: 33250000 wanted: 40000000 > imx-ipuv3 40000000.ipu: clk_di_round_rate: inrate: 133000000 div: 0x00000040 > outrate: 33250000 wanted: 33250000 > imx-ipuv3 40000000.ipu: clk_di_set_rate: inrate: 133000000 desired: 33250000 > div: 0x00000040 > > See an attached oscillogram F0001TEK.jpg. > > So, I want to review this from developers and wait for comments. >
We may need some flag in the devicetree to specify whether the fractional divider can be used or not. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
