Re: [PATCH v2 04/12] driver: clk: imx: Add clock driver for imx6sll

[Stephen Boyd <sboyd@codeaurora.org>]

On 01/10, Jacky Bai wrote:
> 
> > 
> > > +#include <linux/types.h>
> > > +
> > > +#include "clk.h"
> > > +
> > > +#define CCM_ANALOG_PLL_BYPASS		(0x1 << 16)
> > > +#define BM_CCM_CCDR_MMDC_CH0_MASK	(0x2 << 16)
> > > +#define CCDR	0x4
> > > +#define xPLL_CLR(offset)		 (offset + 0x8)
> > > +
> > > +static const char *pll_bypass_src_sels[] = { "osc", "dummy", };
> > 
> > All these should be const char * const unless something is wrong.
> 
> If changed to 'const char * const', it vill has argument type mismatch error, as imx_clk_* wrapper function
> has argument type 'const char *'. 

Hmm that's unfortunate.

> 
> > 
> > > +static const char *pll1_bypass_sels[] = { "pll1", "pll1_bypass_src",
> > > +}; static const char *pll2_bypass_sels[] = { "pll2",
> > > +"pll2_bypass_src", }; static const char *pll3_bypass_sels[] = {
> > > +"pll3", "pll3_bypass_src", }; static const char *pll4_bypass_sels[] =
> > > +{ "pll4", "pll4_bypass_src", }; static const char *pll5_bypass_sels[]
> > > += { "pll5", "pll5_bypass_src", }; static const char
> > > +*pll6_bypass_sels[] = { "pll6", "pll6_bypass_src", };
> > [...]
> > > +	clks[IMX6SLL_CLK_USDHC3]	= imx_clk_gate2("usdhc3",
> > 	"usdhc3_podf",	 base + 0x80,	6);
> > > +
> > > +	/* mask handshake of mmdc */
> > > +	writel_relaxed(BM_CCM_CCDR_MMDC_CH0_MASK, base + CCDR);
> > > +
> > > +	for (i = 0; i < ARRAY_SIZE(clks); i++)
> > > +		if (IS_ERR(clks[i]))
> > > +			pr_err("i.MX6SLL clk %d: register failed with %ld\n", i,
> > > +PTR_ERR(clks[i]));
> > > +
> > > +	clk_data.clks = clks;
> > > +	clk_data.clk_num = ARRAY_SIZE(clks);
> > > +	of_clk_add_provider(np, of_clk_src_onecell_get, &clk_data);
> > > +
> > > +	/* set perclk to from OSC */
> > > +	clk_set_parent(clks[IMX6SLL_CLK_PERCLK_SEL],
> > clks[IMX6SLL_CLK_OSC]);
> > 
> > Can this be done with assigned-clocks in DT?
> 
> Ok, I will move it to assigned-clocks in DT.
> 
> > 
> > > +
> > > +	for (i = 0; i < ARRAY_SIZE(clks_init_on); i++)
> > > +		clk_prepare_enable(clks[clks_init_on[i]]);
> > 
> > Critical clocks?
> 
> Yes, these clocks must be always on. 
> 
> > 
> > > +
> > > +	if (IS_ENABLED(CONFIG_USB_MXS_PHY)) {
> > > +		clk_prepare_enable(clks[IMX6SLL_CLK_USBPHY1_GATE]);
> > > +		clk_prepare_enable(clks[IMX6SLL_CLK_USBPHY2_GATE]);
> > 
> > The phy driver can't enable these?
> 
> The reason why we enable these two clks here is in below commit
> commit a5120e89e7e187a91852896f586876c7a2030804
> Author: Peter Chen <peter.chen@freescale.com>
> Date:   Fri Jan 18 10:38:05 2013 +0800
>       ARM i.MX6: change mxs usbphy clock usage
> 

So can we mark these clks with CLK_IS_CRITICAL flag then instead?
Or are they disabled out of the bootloader?

> > 
> > > +	}
> > > +
> > > +	/* Lower the AHB clock rate before changing the clock source. */
> > > +	clk_set_rate(clks[IMX6SLL_CLK_AHB], 99000000);
> > > +
> > > +	/* Change periph_pre clock to pll2_bus to adjust AXI rate to 264MHz */
> > > +	clk_set_parent(clks[IMX6SLL_CLK_PERIPH_CLK2_SEL],
> > clks[IMX6SLL_CLK_PLL3_USB_OTG]);
> > > +	clk_set_parent(clks[IMX6SLL_CLK_PERIPH],
> > clks[IMX6SLL_CLK_PERIPH_CLK2]);
> > > +	clk_set_parent(clks[IMX6SLL_CLK_PERIPH_PRE],
> > clks[IMX6SLL_CLK_PLL2_BUS]);
> > > +	clk_set_parent(clks[IMX6SLL_CLK_PERIPH],
> > > +clks[IMX6SLL_CLK_PERIPH_PRE]);
> > > +
> > > +	clk_set_rate(clks[IMX6SLL_CLK_AHB], 132000000);
> > 
> > assigned-clocks for rates now? Or perhaps we shouldn't be exposing these as
> > clks if they have some sort of complicated rate sequence switch that we can't
> > guarantee with the clk_ops we have today.
> 
> These clks will be used by some peripherals, so we need to expose these clocks.
> And the above parent and rate swith sequence is not very easy to be handled in assigned-clocks,
> So we leave it in this place. 
> 

How do we guarantee that the rate switch doesn't happen later on,
requiring this coordinated sequence of clk operations?

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