Re: [RFC v1 6/7] clk: meson: meson8b: add support for more M/N values in sys_pll

[Jerome Brunet]

On Wed, 2018-11-14 at 23:57 +0100, Martin Blumenstingl wrote:
> The sys_pll on the EC-100 board is configured to 1584MHz at boot
> (either by u-boot, firmware or chip defaults). This is achieved by using
> M = 66, N = 1 (24MHz * 66 / 1).
> At boot the CPU clock is running off sys_pll divided by 2 which results
> in 792MHz. Thus M = 66 is considered to be a "safe" value for Meson8b.
> 
> To achieve 1608MHz (one of the CPU OPPs on Meson8 and Meson8m2) we need
> M = 67, N = 1. I ran "stress --cpu 4" while infinitely cycling through
> all available frequencies on my Meson8m2 board and could not spot any
> issues with this setting (after ~12 hours of running this).
> 
> On Meson8, Meson8b and Meson8m2 we also want to be able to use 408MHz
> and 816MHz CPU frequencies. These can be achieved by dividing sys_pll by
> 4 (for 408MHz) or 2 (for 816MHz). That means that sys_pll has to run at
> 1632MHz which can be generated using M = 68, N = 1.
> Similarily we also want to be able to use 1008MHz as CPU frequency. This
> means that sys_pll has to run either at 1008MHz or 2016MHz. The former
> would result in an M value of 42, which is lower than the smallest value
> used by the 3.10 GPL kernel sources from Amlogic (50 is the lower limit
> there). Thus we need to run sys_pll at 2016MHz which can ge generated
> using M = 84, N = 1.
> I tested M = 68 and M = 84 on my Meson8b Odroid-C1 and my Meson8m2 board
> by running "stress --cpu 4" while infinitely cycling thorugh all
> available frequencies. I could not spot any issues after ~12 hours of
> running this.
> 
> Amlogic's 3.10 GPL kernel sources have more M/N combinations. I did not
> add them yet because M = 74 (to achieve close to 1800MHz on Meson8) and
> M = 82 (to achieve close to 1992MHz on Meson8 as well) caused my
> Meson8m2 board to hang randomly. It's not clear why this is (for example
> because the board's voltage regulator design is bad, some missing bits
> for these values in our clk-pll driver, etc.). Thus the following M
> values from the Amlogic 3.10 GPL kernel sources are skipped as of now:
> 69, 70, 71, 72, 73, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98
> 
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx>
> ---
>  drivers/clk/meson/meson8b.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/clk/meson/meson8b.c b/drivers/clk/meson/meson8b.c
> index d566dd5bc567..c06a1a7faa4c 100644
> --- a/drivers/clk/meson/meson8b.c
> +++ b/drivers/clk/meson/meson8b.c
> @@ -43,6 +43,11 @@ static const struct pll_params_table
> sys_pll_params_table[] = {
>  	PLL_PARAMS(62, 1),
>  	PLL_PARAMS(63, 1),
>  	PLL_PARAMS(64, 1),
> +	PLL_PARAMS(65, 1),
> +	PLL_PARAMS(66, 1),
> +	PLL_PARAMS(67, 1),
> +	PLL_PARAMS(68, 1),
> +	PLL_PARAMS(84, 1),
>  	{ /* sentinel */ },
>  };
>  

Acked-by: Jerome Brunet <jbrunet@xxxxxxxxxxxx>