On Mon, Sep 22, 2014 at 9:15 PM, Ian Campbell <i...@hellion.org.uk> wrote: > On Mon, 2014-09-22 at 20:47 +0800, Chen-Yu Tsai wrote: >> On Mon, Sep 22, 2014 at 2:35 AM, Ian Campbell <i...@hellion.org.uk> wrote: >> > On Mon, 2014-09-08 at 21:28 +0800, Chen-Yu Tsai wrote: >> >> + /* Set PLL ldo voltage without this PLL6 does not work properly */ >> > >> > Is "this" here the doing it 3 times bit? If that's deliberate then >> > please say so explicitly. e.g. "Set PLL LDO voltage 3 times, without ... >> > etc"), if it's not deliberate then please fix ;-) >> >> Hans, if you could enlighten us? :) >> >> > I'm assuming this is one of those "no docs, allwinner code did it but >> > nobody knows why it works" scenarios. Of course if the reason is >> > known/doc'd then please add a reference. >> >> I looked at the boot1 sources we recently got. >> >> First it sets PRCM_PLL_CTRL_LDO_KEY to enable write access to the other >> values. >> >> Then it sets PRCM_PLL_CTRL_IN_PWR_HIGH (which is the default) and >> PRCM_PLL_CTRL_LDO_OUT_L(1140) in one call. >> >> Then it busy loops for some time to wait for it to stabilize. > > My guess would be that 3 writes happens to cause enough time to pass > that things have (often!) stabilised, which is certainly not as good as > an explicit waiting busy loop. But as you say lets see what Hans says.
FYI I'm dropping this part from the patch, so this discussion is for future reference. :) >> >> + writel(PRCM_PLL_CTRL_LDO_DIGITAL_EN | PRCM_PLL_CTRL_LDO_ANALOG_EN | >> >> + PRCM_PLL_CTRL_EXT_OSC_EN | PRCM_PLL_CTRL_LDO_OUT_L(1140) | >> >> + PRCM_PLL_CTRL_LDO_KEY, &prcm->pll_ctrl1); >> >> + writel(PRCM_PLL_CTRL_LDO_DIGITAL_EN | PRCM_PLL_CTRL_LDO_ANALOG_EN | >> >> + PRCM_PLL_CTRL_EXT_OSC_EN | PRCM_PLL_CTRL_LDO_OUT_L(1140) | >> >> + PRCM_PLL_CTRL_LDO_KEY, &prcm->pll_ctrl1); >> >> + writel(PRCM_PLL_CTRL_LDO_DIGITAL_EN | PRCM_PLL_CTRL_LDO_ANALOG_EN | >> >> + PRCM_PLL_CTRL_EXT_OSC_EN | PRCM_PLL_CTRL_LDO_OUT_L(1140), >> >> + &prcm->pll_ctrl1); >> > [...] _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
