linux-kernel - Re: [PATCH v2 1/6] clk: sunxi-ng: nkm: Support constraints on m/n ratio and parent rate

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Message-ID: <2717565.mvXUDI8C0e@jernej-laptop>
Date: Mon, 05 Feb 2024 18:45:27 +0100
From: Jernej Škrabec <jernej.skrabec@...il.com>
To: Michael Turquette <mturquette@...libre.com>,
 Stephen Boyd <sboyd@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
 Samuel Holland <samuel@...lland.org>,
 Guido Günther <agx@...xcpu.org>,
 Purism Kernel Team <kernel@...i.sm>, Ondrej Jirman <megi@....cz>,
 Neil Armstrong <neil.armstrong@...aro.org>,
 Jessica Zhang <quic_jesszhan@...cinc.com>, Sam Ravnborg <sam@...nborg.org>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Frank Oltmanns <frank@...manns.dev>
Cc: linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
 Frank Oltmanns <frank@...manns.dev>
Subject:
 Re: [PATCH v2 1/6] clk: sunxi-ng: nkm: Support constraints on m/n ratio and
 parent rate

Dne ponedeljek, 05. februar 2024 ob 16:22:24 CET je Frank Oltmanns napisal(a):
> The Allwinner A64 manual lists the following constraints for the
> PLL-MIPI clock:
>  - M/N <= 3
>  - (PLL_VIDEO0)/M >= 24MHz
> 
> The PLL-MIPI clock is implemented as ccu_nkm. Therefore, add support for
> these constraints.
> 
> Signed-off-by: Frank Oltmanns <frank@...manns.dev>

Haven't we discussed that this patch is unnecessary because same effect can
be reached by limiting minimum frequency?

Best regards,
Jernej

> ---
>  drivers/clk/sunxi-ng/ccu_nkm.c | 21 +++++++++++++++++++++
>  drivers/clk/sunxi-ng/ccu_nkm.h |  2 ++
>  2 files changed, 23 insertions(+)
> 
> diff --git a/drivers/clk/sunxi-ng/ccu_nkm.c b/drivers/clk/sunxi-ng/ccu_nkm.c
> index 853f84398e2b..1168d894d636 100644
> --- a/drivers/clk/sunxi-ng/ccu_nkm.c
> +++ b/drivers/clk/sunxi-ng/ccu_nkm.c
> @@ -16,6 +16,20 @@ struct _ccu_nkm {
>  	unsigned long	m, min_m, max_m;
>  };
>  
> +static bool ccu_nkm_is_valid_rate(struct ccu_common *common, unsigned long parent,
> +				  unsigned long n, unsigned long m)
> +{
> +	struct ccu_nkm *nkm = container_of(common, struct ccu_nkm, common);
> +
> +	if (nkm->max_m_n_ratio && (m > nkm->max_m_n_ratio * n))
> +		return false;
> +
> +	if (nkm->min_parent_m_ratio && (parent < nkm->min_parent_m_ratio * m))
> +		return false;
> +
> +	return true;
> +}
> +
>  static unsigned long ccu_nkm_find_best_with_parent_adj(struct ccu_common *common,
>  						       struct clk_hw *parent_hw,
>  						       unsigned long *parent, unsigned long rate,
> @@ -31,6 +45,10 @@ static unsigned long ccu_nkm_find_best_with_parent_adj(struct ccu_common *common
>  				unsigned long tmp_rate, tmp_parent;
>  
>  				tmp_parent = clk_hw_round_rate(parent_hw, rate * _m / (_n * _k));
> +
> +				if (!ccu_nkm_is_valid_rate(common, tmp_parent, _n, _m))
> +					continue;
> +
>  				tmp_rate = tmp_parent * _n * _k / _m;
>  
>  				if (ccu_is_better_rate(common, rate, tmp_rate, best_rate) ||
> @@ -64,6 +82,9 @@ static unsigned long ccu_nkm_find_best(unsigned long parent, unsigned long rate,
>  	for (_k = nkm->min_k; _k <= nkm->max_k; _k++) {
>  		for (_n = nkm->min_n; _n <= nkm->max_n; _n++) {
>  			for (_m = nkm->min_m; _m <= nkm->max_m; _m++) {
> +				if (!ccu_nkm_is_valid_rate(common, parent, _n, _m))
> +					continue;
> +
>  				unsigned long tmp_rate;
>  
>  				tmp_rate = parent * _n * _k / _m;
> diff --git a/drivers/clk/sunxi-ng/ccu_nkm.h b/drivers/clk/sunxi-ng/ccu_nkm.h
> index 6601defb3f38..c409212ee40e 100644
> --- a/drivers/clk/sunxi-ng/ccu_nkm.h
> +++ b/drivers/clk/sunxi-ng/ccu_nkm.h
> @@ -27,6 +27,8 @@ struct ccu_nkm {
>  	struct ccu_mux_internal	mux;
>  
>  	unsigned int		fixed_post_div;
> +	unsigned long		max_m_n_ratio;
> +	unsigned long		min_parent_m_ratio;
>  
>  	struct ccu_common	common;
>  };
> 
>