linux-kernel - Re: [PATCH v3 13/15] clk: samsung: Implement manual PLL control for ARM64 SoCs

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Message-ID: <eb968e2b-495b-44dd-aad9-3cd5eac72bdf@linaro.org>
Date: Sun, 25 Feb 2024 17:09:43 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Sam Protsenko <semen.protsenko@...aro.org>,
 Sylwester Nawrocki <s.nawrocki@...sung.com>,
 Chanwoo Choi <cw00.choi@...sung.com>
Cc: Alim Akhtar <alim.akhtar@...sung.com>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd
 <sboyd@...nel.org>, Rob Herring <robh@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Tomasz Figa <tomasz.figa@...il.com>,
 linux-samsung-soc@...r.kernel.org, linux-clk@...r.kernel.org,
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 13/15] clk: samsung: Implement manual PLL control for
 ARM64 SoCs

On 24/02/2024 21:20, Sam Protsenko wrote:
> Some ARM64 Exynos chips are capable to control PLL clocks automatically.
> For those chips, whether the PLL is controlled automatically or manually
> is chosen in PLL_CON1 register with next bits:
> 
>     [28]  ENABLE_AUTOMATIC_CLKGATING
>     [1]   MANUAL_PLL_CTRL
>     [0]   AUTO_PLL_CTRL
> 
> The bl2 bootloader sets 0x10000001 value for some PLL_CON1 registers,
> which means any attempt to control those PLLs manually (e.g.
> disabling/enabling those PLLs or changing MUX parent clocks) would lead
> to PLL lock timeout with error message like this:
> 
>     Could not lock PLL ...
> 
> At the moment, all Samsung clock drivers implement manual clock control.
> So in order to make it possible to control PLLs, corresponding PLL_CON1
> registers should be set to 0x2 first.
> 
> Some older ARM64 chips don't implement the automatic clock control
> though. It also might be desirable to configure some PLLs for manual
> control, while keeping the default configuration for the rest. So it'd
> convenient to choose this PLL mode for each CMU separately. Introduce
> .manual_plls field to CMU structure to choose the PLL control mode.
> Because it'll be initialized with "false" in all existing CMU
> structures by default, it won't affect any existing clock drivers,
> allowing for this feature to be enabled gradually when it's needed with
> no change for the rest of users. In case .manual_plls is set, set
> PLL_CON1 registers to manual control, akin to what's already done for
> gate clocks in exynos_arm64_init_clocks(). Of course, PLL_CON1 registers
> should be added to corresponding struct samsung_cmu_info::clk_regs array
> to make sure they get initialized.
> 
> No functional change. This patch adds a feature, but doesn't enable it
> for any users.
> 
> Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>
> ---
> Changes in v3:
>   - none
> 
> Changes in v2:
>   - none
> 
>  drivers/clk/samsung/clk-exynos-arm64.c | 44 +++++++++++++++++---------
>  drivers/clk/samsung/clk.h              |  4 +++
>  2 files changed, 33 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/clk/samsung/clk-exynos-arm64.c b/drivers/clk/samsung/clk-exynos-arm64.c
> index 6fb7194df7ab..55490209b9a9 100644
> --- a/drivers/clk/samsung/clk-exynos-arm64.c
> +++ b/drivers/clk/samsung/clk-exynos-arm64.c
> @@ -25,6 +25,19 @@
>  #define GATE_OFF_START		0x2000
>  #define GATE_OFF_END		0x2fff
>  
> +/* PLL CON register offsets range */
> +#define PLL_CON_START		0x100
> +#define PLL_CON_END		0x600
> +
> +/* PLL register bits */
> +#define PLL_CON1_MANUAL		BIT(1)
> +
> +/* Helper macros to check for particular clock regiter by its offset */
> +#define IS_GATE_REG(o)		((o) >= GATE_OFF_START && (o) <= GATE_OFF_END)
> +#define IS_PLL_CONx_REG(o)	((o) >= PLL_CON_START && (o) <= PLL_CON_END)
> +#define IS_PLL_CON1_REG(o)	\
> +	(IS_PLL_CONx_REG(o) && ((o) & 0xf) == 0x4 && !((o) & 0x10))

These should be static functions, because it leads to trickier code. See
also checkpatch warning.

Best regards,
Krzysztof