Re: [PATCH v2] clk: samsung: exynos4: Enable VPLL and EPLL clocks for suspend/resume cycle

[Chanwoo Choi <cw00.choi@samsung.com>]

Hi Marek,

On 2017년 09월 15일 18:41, Marek Szyprowski wrote:
> Commit 6edfa11cb396 ("clk: samsung: Add enable/disable operation for
> PLL36XX clocks") added enable/disable operations to PLL clocks. Prior that
> VPLL and EPPL clocks were always enabled because the enable bit was never
> touched. Those clocks have to be enabled during suspend/resume cycle,
> because otherwise board fails to enter sleep mode. This patch enables them
> unconditionally before entering system suspend state. System restore
> function will set them to the previous state saved in the register cache
> done before that unconditional enable.
> 
> Fixes: 6edfa11cb396 ("clk: samsung: Add enable/disable operation for PLL36XX clocks")
> CC: stable@vger.kernel.org # v4.13
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
> Changelog:
> v2:
> - wait until PLL is properly locked
> ---
>  drivers/clk/samsung/clk-exynos4.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/clk/samsung/clk-exynos4.c b/drivers/clk/samsung/clk-exynos4.c
> index e40b77583c47..d8d3cb67b402 100644
> --- a/drivers/clk/samsung/clk-exynos4.c
> +++ b/drivers/clk/samsung/clk-exynos4.c
> @@ -294,6 +294,18 @@ enum exynos4_plls {
>  #define PLL_ENABLED	(1 << 31)
>  #define PLL_LOCKED	(1 << 29)
>  
> +static void exynos4_clk_enable_pll(u32 reg)
> +{
> +	u32 pll_con = readl(reg_base + reg);
> +	pll_con |= PLL_ENABLED;
> +	writel(pll_con, reg_base + reg);
> +
> +	while (!(pll_con & PLL_LOCKED)) {
> +		cpu_relax();
> +		pll_con = readl(reg_base + reg);
> +	}
> +}
> +
>  static void exynos4_clk_wait_for_pll(u32 reg)
>  {
>  	u32 pll_con;
> @@ -315,6 +327,9 @@ static int exynos4_clk_suspend(void)
>  	samsung_clk_save(reg_base, exynos4_save_pll,
>  				ARRAY_SIZE(exynos4_clk_pll_regs));
>  
> +	exynos4_clk_enable_pll(EPLL_CON0);
> +	exynos4_clk_enable_pll(VPLL_CON0);
> +

To support runtime pm for Exynos5433 on your patch[1],
You get the clock from device-tree and enable the clock
on the suspend function (exynos5433_cmu_suspend) as following:

[1] [PATCH v9 3/5] clk: samsung: exynos5433: Add support for runtime PM
- https://patchwork.kernel.org/patch/9911753/
------------
static int exynos5433_cmu_suspend(struct device *dev)                                                          
{                                                                                                              
	struct exynos5433_cmu_data *data = dev_get_drvdata(dev);                                               
	int i;                                                                                                 
                                                                                                            
	samsung_clk_save(data->ctx->reg_base, data->clk_save,                                                  
				data->nr_clk_save);                                                                   

	for (i = 0; i < data->nr_pclks; i++)                                                                   
		clk_prepare_enable(data->pclks[i]);                                                            

	samsung_clk_restore(data->ctx->reg_base, data->clk_suspend,                                            
				data->nr_clk_suspend);                                                             

	return 0;
}
------------

IMHO, I think that you better to get the PLL clock from device-tree
instead of adding the duplicate code for enabling PLL(EPLL_CON0/VPLL_CON0).
But, Maybe many -EPROBE_DEFER happen on device driver
if using the 'platform_driver' method instead of CLK_OF_DECLARE macro.

I'm not sure what is more important on below:
- Remove the duplicate code
- Prevent the -EPROBE_DEFER

Anyway, I will follow Sylwester's opinion.


>  	if (exynos4_soc == EXYNOS4210) {
>  		samsung_clk_save(reg_base, exynos4_save_soc,
>  					ARRAY_SIZE(exynos4210_clk_save));
> 

-- 
Best Regards,
Chanwoo Choi
Samsung Electronics