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

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Message-ID: <DB3PR0402MB39160C67665B2A101F2B0885F5ED0@DB3PR0402MB3916.eurprd04.prod.outlook.com>
Date:   Tue, 25 Feb 2020 09:17:29 +0000
From:   Anson Huang <anson.huang@....com>
To:     Daniel Baluta <daniel.baluta@....com>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "sboyd@...nel.org" <sboyd@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        Leonard Crestez <leonard.crestez@....com>,
        Abel Vesa <abel.vesa@....com>, Peng Fan <peng.fan@....com>,
        Jacky Bai <ping.bai@....com>, Andy Duan <fugang.duan@....com>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH 1/4] clk: imx8mn: A53 core clock no need to be critical

Hi, Daniel

> Subject: Re: [PATCH 1/4] clk: imx8mn: A53 core clock no need to be critical
> 
> Hi Anson,
> 
> One comment inline:
> 
> On 25.02.2020 10:49, 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, 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@....com>
> > ---
> >   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]);
> 
> 
> Why do you need to move this code? If there is a reason please add a
> separate patch and explain why.

I have explained the reason in the commit message, maybe NOT detail enough
for you, if these two set parent is put before ARM_CLK register, it will cause ARM_PLL
being disabled as no consumer using it, so the changes must be done in this patch.
After ARM_CLK register done, as it is critical, its parent will be always ON, hence re-parent
is OK. 

Thanks,
Anson

> 
> > -
> >   	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);
>