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

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Date: Tue, 06 Feb 2024 18:51:02 +0100
From: Jernej Škrabec <jernej.skrabec@...il.com>
To: Frank Oltmanns <frank@...manns.dev>
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 3/6] clk: sunxi-ng: nkm: Support minimum and maximum rate

Dne ponedeljek, 05. februar 2024 ob 21:34:04 CET je Frank Oltmanns napisal(a):
> 
> On 2024-02-05 at 18:56:09 +0100, Jernej Škrabec <jernej.skrabec@...il.com> wrote:
> > Dne ponedeljek, 05. februar 2024 ob 16:22:26 CET je Frank Oltmanns napisal(a):
> >> 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.
> >>
> >> 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;
> >
> > Please take a look at ccu_nm_round_rate() code. You need to consider postdiv
> > and you can return immediately.
> 
> There is a difference here insofar that ccu_nm is always connected to a
> fixed rate parent (at least that's my understanding). Therefore, in
> ccu_nm_round_rate() we can be sure that the min or max rate can really
> be set. In ccu_nkm we don't have that luxury, we actually have to find a
> rate that is approximately equal to the min and max rate, based on the
> parent rate. Therefore, we can't return immediately.

Good point.

> 
> Also, I'm not sure what you mean about me needing to consider postdiv.
> That's what I did. The check is after multiplying with the postdiv. It's
> the same as in ccu_nm_round_rate() (just minus the immediate return).

Nevermind, this applies only for immediate return.

Best regards,
Jernej

> 
> >
> >> +
> >>  	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;
> >> +
> >
> > No need for this, clk subsystem calls round rate before setting actual clock
> > rate.
> 
> I'll remove the checks in V3.
> 
> Best regards,
>   Frank
> 
> >
> > Best regards,
> > Jernej
> >
> >>  	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;
> >>
> >>
> >>
>