Hi Fabio, First a disclaimer. I no longer work for the client that had me make this change. I also no longer have any iMX53 hardware to do any kind of tests. But I'm happy to help out with this email.
> Hi Rick and Sebastian, > > On Thu, Feb 15, 2018 at 2:15 PM, Sebastian Reichel > <sebastian.reic...@collabora.co.uk> wrote: > > From: Rick Bronson <r...@efn.org> > > > > Allow higher UART baud rates for communications to ACHC at 13.5 MBaud > > What does ACHC mean? ACHC is an product acronym, probably should change that sentence to: Allow higher UART baud rates for communications up to 13.5 MBaud > > Done in u-boot since it changes a divider common to all UARTs, including > > the console. If it were done in Linux we would get garbled characters > > during the handoff from u-boot to the kernel. > > It would be nice to explain a bit how you achieve the higher baud rates. Background: PLL2 runs at 400 MHz, PLL3 runs at 216 MHz. One of these PLL's are fed to a UART divider, the output of which sets the maximum UART baud rates that are based on these rates divided by 16. Before patch: PLL3 (400 MHz) for UART's, divide by 6, get 66.66 MHz from it. Max baud rate is 4.166 MBaud. After patch: PLL2 (216 MHz), divide by 1, get 216 MHz from it. Max baud rate is 13.5 MBaud. The last I saw this code was 2014 so it's a little fuzzy. Not sure why I didn't keep PLL3 and just change the divider from 6 to 3, that would have allowed a max of 8.33 MBaud and at the time, I was just looking for at least 8 MBaud. > > Looks like you don't use PLL2 as the UART clock anyomore. That's correct, see above. > > Please expland a bit further on the new UART clock sheme. > > > > > Signed-off-by: Sebastian Reichel <sebastian.reic...@collabora.co.uk> > > --- > > arch/arm/mach-imx/mx5/lowlevel_init.S | 4 ++++ > > 1 file changed, 4 insertions(+) > > > > diff --git a/arch/arm/mach-imx/mx5/lowlevel_init.S b/arch/arm/mach-imx/mx5/lowlevel_init.S > > index f5bc6728b7c2..ee4c3afd2fed 100644 > > --- a/arch/arm/mach-imx/mx5/lowlevel_init.S > > +++ b/arch/arm/mach-imx/mx5/lowlevel_init.S > > @@ -319,11 +319,13 @@ setup_pll_func: > > ldr r1, =0x00016154 > > str r1, [r0, #CLKCTL_CBCMR] > > > > +#if !defined(CONFIG_TARGET_MX53PPD) > > It would be better if this option could be a generic one, something > like CONFIG_MX53_SERIAL_HIGHBAUD, so that other boads could use it if > needed. Yes it probably would. Cheers, Rick _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot