linux-kernel - Re: [PATCH v2 3/6] clk: sunxi-ng: nkm: Support minimum and maximum rate

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Message-ID: <8734tmhzkg.fsf@oltmanns.dev>
Date: Wed, 21 Feb 2024 11:38:39 +0100
From: Frank Oltmanns <frank@...manns.dev>
To: Jernej Skrabec <jernej.skrabec@...il.com>, Maxime Ripard
 <mripard@...nel.org>, Diego Roversi <diegor@...cali.it>
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>, 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 3/6] clk: sunxi-ng: nkm: Support minimum and maximum
 rate

Hi Jernej,
hi Maxime,

On 2024-02-05 at 16:22:26 +0100, Frank Oltmanns <frank@...manns.dev> wrote:
> According to the Allwinner User Manual, the Allwinner A64 requires
> PLL-MIPI to run at 500MHz-1.4GHz. Add support for that to ccu_nkm.

I should point out that limiting PLL-MIPI also fixes a regression
that was introduced in 6.5, specifically
ca1170b69968233b34d26432245eddf7d265186b "clk: sunxi-ng: a64: force
select PLL_MIPI in TCON0 mux". This has been bisected and reported by
Diego [1].

I don't know the procedure (yet), but probably the fix (if and when
accepted) should be backported at least to 6.6 (first broken LTS), 6.7
(stable), and 6.8 (next stable).

My suggestion:
 - In V3 of this series, I will reorder the patches, so that what is now
   PATCH 3 and 4 becomes 1 and 2 respectively, so that they can be
   applied to 6.6 more easily.
 - Maxime, IIUC you requested some refactoring for handling the rate
   limits [2]. I propose, we use my current proposal as-is, and I will
   do a follow-up series for the refactoring.

Please let me know how you would like me to proceed.

Thanks,
  Frank

[1]: https://groups.google.com/g/linux-sunxi/c/Rh-Uqqa66bw
[2]: https://lore.kernel.org/all/exb2lvjcozak5fayrgyenrd3ntii4jfxgvqork4klyz5pky2aq@dj2zyw5su6pv/

>
> Signed-off-by: Frank Oltmanns <frank@...manns.dev>
> ---
>  drivers/clk/sunxi-ng/ccu_nkm.c | 13 +++++++++++++
>  drivers/clk/sunxi-ng/ccu_nkm.h |  2 ++
>  2 files changed, 15 insertions(+)
>
> diff --git a/drivers/clk/sunxi-ng/ccu_nkm.c b/drivers/clk/sunxi-ng/ccu_nkm.c
> index 1168d894d636..7d135908d6e0 100644
> --- a/drivers/clk/sunxi-ng/ccu_nkm.c
> +++ b/drivers/clk/sunxi-ng/ccu_nkm.c
> @@ -181,6 +181,12 @@ static unsigned long ccu_nkm_round_rate(struct ccu_mux_internal *mux,
>  	if (nkm->common.features & CCU_FEATURE_FIXED_POSTDIV)
>  		rate *= nkm->fixed_post_div;
>
> +	if (nkm->min_rate && rate < nkm->min_rate)
> +		rate = nkm->min_rate;
> +
> +	if (nkm->max_rate && rate > nkm->max_rate)
> +		rate = nkm->max_rate;
> +
>  	if (!clk_hw_can_set_rate_parent(&nkm->common.hw))
>  		rate = ccu_nkm_find_best(*parent_rate, rate, &_nkm, &nkm->common);
>  	else
> @@ -220,6 +226,13 @@ static int ccu_nkm_set_rate(struct clk_hw *hw, unsigned long rate,
>  	_nkm.min_m = 1;
>  	_nkm.max_m = nkm->m.max ?: 1 << nkm->m.width;
>
> +
> +	if (nkm->min_rate && rate < nkm->min_rate)
> +		rate = nkm->min_rate;
> +
> +	if (nkm->max_rate && rate > nkm->max_rate)
> +		rate = nkm->max_rate;
> +
>  	ccu_nkm_find_best(parent_rate, rate, &_nkm, &nkm->common);
>
>  	spin_lock_irqsave(nkm->common.lock, flags);
> diff --git a/drivers/clk/sunxi-ng/ccu_nkm.h b/drivers/clk/sunxi-ng/ccu_nkm.h
> index c409212ee40e..358a9df6b6a0 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		min_rate;
> +	unsigned long		max_rate;
>  	unsigned long		max_m_n_ratio;
>  	unsigned long		min_parent_m_ratio;