RE: [PATCH 1/4] clk: imx8mn: A53 core clock no need to be critical

[Anson Huang]

Hi, Shawn

> Subject: Re: [PATCH 1/4] clk: imx8mn: A53 core clock no need to be critical
> 
> On Tue, Feb 25, 2020 at 04:49:11PM +0800, Anson Huang wrote:
> > 'A53_CORE' is just a mux and no need to be critical, being critical
> > will cause its parent clock always ON which does NOT make sense,
> 
> I do not quite understand what problem this patch is trying to fix.  In the end,
> all the ancestor clocks of "arm", including "arm_a53_core" will still be ON, as
> "arm" has CLK_IS_CRITICAL flag.  What is the difference you are trying to
> make here?

This patch actually is to fix the clock parent switch flow of A53, previous flow is incorrect,
the reason why it works is the IMX8MN_CLK_A53_CORE is marked as CRITICAL,
but if with correct flow of parent switch, the "arm" as CLK_IS_CRITICAL flag is enough and
IMX8MN_CLK_A53_CORE will be enabled because it is "arm" clk's parent.

The A53 clock parent switch should be put after the "arm" clk creation, then no need to have
CLK_IS_CRITICAL flag for IMX8MN_CLK_A53_CORE, and its usecount will be 1 as expected.
Previous implementation will has use count equal 2 which is incorrect.

Anson

> 
> Shawn
> 
> > to make sure CPU's hardware clock source NOT being disabled during
> > clock tree setup, need to move the 'A53_SRC'/'A53_CORE' reparent
> > operations to after critical clock 'ARM_CLK' setup finished.
> >
> > Signed-off-by: Anson Huang <Anson.Huang@xxxxxxx>
> > ---
> >  drivers/clk/imx/clk-imx8mn.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/clk/imx/clk-imx8mn.c
> > b/drivers/clk/imx/clk-imx8mn.c index 83618af..0bc7070 100644
> > --- a/drivers/clk/imx/clk-imx8mn.c
> > +++ b/drivers/clk/imx/clk-imx8mn.c
> > @@ -428,7 +428,7 @@ static int imx8mn_clocks_probe(struct
> platform_device *pdev)
> >  	hws[IMX8MN_CLK_GPU_SHADER_DIV] =
> hws[IMX8MN_CLK_GPU_SHADER];
> >
> >  	/* CORE SEL */
> > -	hws[IMX8MN_CLK_A53_CORE] =
> imx_clk_hw_mux2_flags("arm_a53_core", base + 0x9880, 24, 1,
> imx8mn_a53_core_sels, ARRAY_SIZE(imx8mn_a53_core_sels),
> CLK_IS_CRITICAL);
> > +	hws[IMX8MN_CLK_A53_CORE] = imx_clk_hw_mux2("arm_a53_core",
> base +
> > +0x9880, 24, 1, imx8mn_a53_core_sels,
> > +ARRAY_SIZE(imx8mn_a53_core_sels));
> >
> >  	/* BUS */
> >  	hws[IMX8MN_CLK_MAIN_AXI] =
> > imx8m_clk_hw_composite_critical("main_axi", imx8mn_main_axi_sels,
> base
> > + 0x8800); @@ -559,15 +559,15 @@ static int imx8mn_clocks_probe(struct
> > platform_device *pdev)
> >
> >  	hws[IMX8MN_CLK_DRAM_ALT_ROOT] =
> > imx_clk_hw_fixed_factor("dram_alt_root", "dram_alt", 1, 4);
> >
> > -	clk_hw_set_parent(hws[IMX8MN_CLK_A53_SRC],
> hws[IMX8MN_SYS_PLL1_800M]);
> > -	clk_hw_set_parent(hws[IMX8MN_CLK_A53_CORE],
> hws[IMX8MN_ARM_PLL_OUT]);
> > -
> >  	hws[IMX8MN_CLK_ARM] = imx_clk_hw_cpu("arm", "arm_a53_core",
> >  					   hws[IMX8MN_CLK_A53_CORE]->clk,
> >  					   hws[IMX8MN_CLK_A53_CORE]->clk,
> >  					   hws[IMX8MN_ARM_PLL_OUT]->clk,
> >  					   hws[IMX8MN_CLK_A53_DIV]->clk);
> >
> > +	clk_hw_set_parent(hws[IMX8MN_CLK_A53_SRC],
> hws[IMX8MN_SYS_PLL1_800M]);
> > +	clk_hw_set_parent(hws[IMX8MN_CLK_A53_CORE],
> > +hws[IMX8MN_ARM_PLL_OUT]);
> > +
> >  	imx_check_clk_hws(hws, IMX8MN_CLK_END);
> >
> >  	ret = of_clk_add_hw_provider(np, of_clk_hw_onecell_get,
> > clk_hw_data);
> > --
> > 2.7.4
> >