[U-Boot] [PATCH] davinci: omapl138_lcdk: fix PLL0 frequency

[Sekhar Nori]

Hi David,

On Thursday 15 March 2018 07:06 AM, David Lechner wrote:
> commit 1601dd97edc6 ("davinci: omapl138_lcdk: increase PLL0 frequency")
> changed the PLL0 frequency to 456MHz, which is needed for the LCDC IP
> block. However, in doing so, it caused the PLLOUT clock to be outside
> of the allowable specifications given in the OMAP-L138 data sheet. (It
> says PLLOUT must be 600MHz max). It also uses a PLLM value outside of
> the range given in the TRM (it says PLLM must in the range 0 to 0x1f).
> 
> So here is what we have currently:
> 
> PLLOUT = 24 / (0 + 1) * (37 + 1) = 912MHz (out of spec)
>          ^     ^         ^
>        CLKIN PREDIV    PLLM (out of spec)
> 
> input to PLLDIVn = 912 / (1 + 1) = 456MHz (desired result)
>                     ^     ^
>                  PLLOUT POSTDIV
> 
> This changes the PLLM value to 18 and the POSTDIV value to 0 so that
> PLLOUT is now within specification but we still get the desired
> result.
> 
> PLLOUT = 24 / (0 + 1) * (18 + 1) = 456MHz (within spec)
>          ^     ^         ^
>        CLKIN PREDIV     PLLM
> 
> input to PLLDIVn = 456 / (0 + 1) = 456MHz (desired result)
>                     ^     ^
>                  PLLOUT POSTDIV
> 
> Fixes: 1601dd97edc6 ("davinci: omapl138_lcdk: increase PLL0 frequency")
> Signed-off-by: David Lechner <david at lechnology.com>

Thanks for the patch and great description. It looks correct to me.
Hopefully I can provide some testing feedback too soon.

> ---
> 
> FYI, I haven't been able to test this patch yet. The changes affect the SPL
> image, which has to be flashed to SPI. I am having trouble with the flash
> utility[1] running on Linux. It gets stuck at:
> 
>    0% [ ------------------------------------------------------------ ]
>                 Programming application into flash...
> 
> So, if anyone has some advice on how to make it work or can test the patch,
> that would be helpful.

The easiest thing to do would be to shift to MMC/SD boot so you can
easily update images.

Before starting though, I would take note of out-of-the-box boot switch
settings and also take a disk image backup of the SD card. Or better
yet, just use another SD card.

Setup the SW1 dip switch thus:
http://processors.wiki.ti.com/index.php/How_to_boot_OMAP-L138_LCDK_from_SD_card#Settings_DIP_switches_to_SD.2FMMC_boot_mode

Prepare an SD card for boot:

$ sudo dd if=u-boot.ais of=/dev/sd<N> seek=117 bs=512 conv=fsync

Thanks,
Sekhar