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

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Date: Mon, 05 Feb 2024 18:50:27 +0100
From: Frank Oltmanns <frank@...manns.dev>
To: Jernej Škrabec <jernej.skrabec@...il.com>
Cc: 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>, 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
Subject: Re: [PATCH v2 1/6] clk: sunxi-ng: nkm: Support constraints on m/n
 ratio and parent rate

Hi Jernej,

On 2024-02-05 at 18:45:27 +0100, Jernej Škrabec <jernej.skrabec@...il.com> wrote:
> 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?

The patch for ccu_nm was unnecessary:
https://lore.kernel.org/all/87jzoug2jz.fsf@oltmanns.dev/

Unfortunately, we still need this one.

Best regards,
  Frank

>
> 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;
>>  };
>>
>>