[PATCH] clk: vf610: don't stop enabled clocks in suspend

[Stefan Agner]

Hi Sergei,

If all peripherals which do not act as wakeup source disable clocks
explicily, this would be the right approach. However, currently not all
of them do, hence this patch will raise the energy consumption during
sleep modes. The peripherals of course rely on the clock driver to
restore the state (gates) at wake-up time, but I think that is how it
works for most SoCs anyway.

In the Toradex branch I came up with a solution which allows to
selectively define which clock should be disabled and which should be
left on by the hardware:
http://git.toradex.com/cgit/linux-toradex.git/commit/?h=toradex_vf_4.1-next&id=66e003c1ad2acdaa7d42e1113add7d44479392ab

I then started to fix some peripherals so that they explicitly disable
clock if wakeup is not enabled. I changed those clocks so they do not
get automatically disabled:
http://git.toradex.com/cgit/linux-toradex.git/commit/?h=toradex_vf_4.1-next&id=fc60861b91c6585740e9a502fa4008b2f4694b22

I plan to upstream those changes but did not came around to put
toghether a rebased and cleaned up patchset so far.

--
Stefan

On 2015-10-16 07:51, Sergei Miroshnichenko wrote:
> Currently Vybrid Clock Gating is configured to turn off all clocks in stop
> mode, while kernel assumes them enabled unless explicitly disabled. This
> behavior prevents waking up from wakeup sources.
> 
> Fix this by replacing Clock Gating Register bitmask 3 (Clock is on during
> all modes, except stop mode) with bitmask 2 (Clock is on during all modes,
> even stop mode): refer to Vybrid Reference Manual Chapter 10 "Clock
> Controller Module (CCM)".
> 
> Tested on a VF610-based board.
> 
> Signed-off-by: Sergei Miroshnichenko <sergeimir at emcraft.com>
> ---
>  drivers/clk/imx/clk-gate2.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/clk/imx/clk-gate2.c b/drivers/clk/imx/clk-gate2.c
> index 8935bff..ac35d75 100644
> --- a/drivers/clk/imx/clk-gate2.c
> +++ b/drivers/clk/imx/clk-gate2.c
> @@ -50,7 +50,8 @@ static int clk_gate2_enable(struct clk_hw *hw)
>  		goto out;
>  
>  	reg = readl(gate->reg);
> -	reg |= 3 << gate->bit_idx;
> +	reg &= ~(3 << gate->bit_idx);
> +	reg |= 2 << gate->bit_idx;
>  	writel(reg, gate->reg);
>  
>  out:
> @@ -86,7 +87,7 @@ static int clk_gate2_reg_is_enabled(void __iomem
> *reg, u8 bit_idx)
>  {
>  	u32 val = readl(reg);
>  
> -	if (((val >> bit_idx) & 1) == 1)
> +	if (((val >> bit_idx) & 3) == 2)
>  		return 1;
>  
>  	return 0;