On Thu, Jun 28, 2018 at 10:30 AM, Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> wrote: > On Wed, Jun 27, 2018 at 04:07:11PM +0200, Mogens Lauridsen wrote: >> PLL3 was first set to 400MHz and then some peripheral was switched >> to PLL3. Finally PLL3 was set to 216MHz. This could make some >> i.MX538 hang in a dead loop in the boot process. > > Let's see what the code currently does: > > By reset default the clock path to the DDR is: > > PLL2 (192MHz) -> periph_clk -> main_bus_clk -> axi_a_podf -> axi_a (/1 = 192MHz) -> ddr_clk_root > > PLL2 is running at 192MHz. The code now tries to switch PLL2 from 192MHz > to 400MHz. This requires that the RAM is driven by some other clock > during > the PLL reconfiguration. The code switches the clock path to: > > PLL3 (400MHz) -> periph_clk -> main_bus_clk -> axi_a_podf -> axi_a (/2 = 200MHz) -> ddr_clk_root > > Then PLL2 is reconfigured to 400MHz and the DDR clock path is switched > back to the original path, this time with the PLL runnning at 400MHz, so > RAM is then running at the desired speed. > > The code configures PLL3 to 400MHz probably to keep the DDR frequency > nearly constant during the transition. > > I have no idea why your change helps you. When I understand correctly > then you are running nearly at half the frequency during the transition > (400/216). > > I'm afraid to merge such change as long as we do not fully understand > what we are doing and why it helps. I see your point. I don't know exactly why it helps. But to me it looks suspicious to set a clock to 400MHz which in the end only is suppose to run at 216 MHz. I fear that there are small differences in the individual iMX538 and in some of them the pll might not always be able to get a lock at the high frequency. The problem seem to have some relationship with the temperature of the chip. (Higher temperature also seem to solve the problem). > > BTW the current code is the same as on U-Boot which is derived from the > original Freescale code, so this is not exactly new or barebox specific. Yes, I did see that the code has been in barebox since 2011. I am also puzzled why we see this, and nobody else has seen/reported it. We are using the i.MX538 which is in a pop package with the DDR mounted on the top of the i.MX. This chip might not be widely used. > > Do you have anything special in your dcd table that influences the > clocks in an unexpected way? Not as far as I know. Could you give me a hint of what I should look for? Best regards, Mogens > > 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 | _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
