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

[Peter Howard]

On Wed, 2018-03-14 at 20:36 -0500, 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>
> ---
> 
> 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.
> 

I have done a first-pass sanity check and it works.  However the
current default setup is not what I have been using (this is the first
time in some months I've done anything on the LCDK) and I haven't
booted out of u-boot, so I wouldn't call this "works perfectly".  I'll
do some more serious testing over the weekend.

Cross-compile toolchain:
  gcc version 7.2.1 20171011 (Linaro GCC 7.2-2017.11)

Flash command:
  mono sfh_OMAP-L138.exe -flash_noubl -targetType OMAPL138_LCDK -flashType NAND -p /dev/ttyUSB1 u-boot.ais

Console output on boot:
  U-Boot SPL 2018.03-00068-g218da80-dirty (Mar 15 2018 - 21:15:08 +1100)
  Trying to boot from NAND

  U-Boot SPL 2018.03-00068-g218da80-dirty (Mar 15 2018 - 21:15:08 +1100)
  Trying to boot from NAND

  U-Boot SPL 2018.03-00068-g218da80-dirty (Mar 15 2018 - 21:15:08 +1100)
  Trying to boot from NAND

(As I don't have anything set up on NAND the cycling is to be expected)
 
> However, the bootloader on my LCDK is using these values already, so
> I expect
> this to work as advertized.
> 
> [1]: http://processors.wiki.ti.com/index.php/Serial_Boot_and_Flash_Lo
> ading_Utility_for_OMAP-L138
> 
> 
>  configs/omapl138_lcdk_defconfig | 1 +
>  include/configs/omapl138_lcdk.h | 3 ++-
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/configs/omapl138_lcdk_defconfig
> b/configs/omapl138_lcdk_defconfig
> index ccb308b..0a2af11 100644
> --- a/configs/omapl138_lcdk_defconfig
> +++ b/configs/omapl138_lcdk_defconfig
> @@ -2,6 +2,7 @@ CONFIG_ARM=y
>  CONFIG_ARCH_DAVINCI=y
>  CONFIG_SYS_TEXT_BASE=0xc1080000
>  CONFIG_TARGET_OMAPL138_LCDK=y
> +CONFIG_SYS_DA850_PLL0_POSTDIV=0
>  CONFIG_SYS_DA850_PLL1_PLLDIV3=0x8003
>  CONFIG_TI_COMMON_CMD_OPTIONS=y
>  CONFIG_SPL_LIBCOMMON_SUPPORT=y
> diff --git a/include/configs/omapl138_lcdk.h
> b/include/configs/omapl138_lcdk.h
> index ea7bdf1..1e1c66b 100644
> --- a/include/configs/omapl138_lcdk.h
> +++ b/include/configs/omapl138_lcdk.h
> @@ -57,7 +57,8 @@
>   * PLL configuration
>   */
>  
> -#define CONFIG_SYS_DA850_PLL0_PLLM     37
> +/* Requires CONFIG_SYS_DA850_PLL0_POSTDIV=0, set in Kconfig */
> +#define CONFIG_SYS_DA850_PLL0_PLLM     18
>  #define CONFIG_SYS_DA850_PLL1_PLLM     21
>  
>  /*

-- 
Peter Howard <pjh at northern-ridge.com.au>

(also <phoward at gme.net.au>)
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