linux-kernel - Re: [PATCH 4/5] clk: sunxi-ng: a64: Add constraints on PLL-VIDEO0's n/m ratio

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Message-ID: <3461075.QJadu78ljV@jernej-laptop>
Date: Tue, 09 Jan 2024 21:29:39 +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>,
 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
Subject:
 Re: [PATCH 4/5] clk: sunxi-ng: a64: Add constraints on PLL-VIDEO0's n/m ratio

Dne nedelja, 31. december 2023 ob 10:10:40 CET je Frank Oltmanns napisal(a):
> 
> On 2023-12-19 at 17:54:19 +0100, Jernej Škrabec <jernej.skrabec@...il.com> wrote:
> > Dne ponedeljek, 18. december 2023 ob 14:35:22 CET je Frank Oltmanns napisal(a):
> >> The Allwinner A64 manual lists the following constraint for the
> >> PLL-VIDEO0 clock: 8 <= N/M <= 25
> >>
> >> Use this constraint.
> >>
> >> Signed-off-by: Frank Oltmanns <frank@...manns.dev>
> >> ---
> >>  drivers/clk/sunxi-ng/ccu-sun50i-a64.c | 8 ++++++--
> >>  1 file changed, 6 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/clk/sunxi-ng/ccu-sun50i-a64.c b/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
> >> index c034ac027d1c..75d839da446c 100644
> >> --- a/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
> >> +++ b/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
> >> @@ -68,7 +68,8 @@ static SUNXI_CCU_NM_WITH_SDM_GATE_LOCK(pll_audio_base_clk, "pll-audio-base",
> >>  				       BIT(28),	/* lock */
> >>  				       CLK_SET_RATE_UNGATE);
> >>
> >> -static SUNXI_CCU_NM_WITH_FRAC_GATE_LOCK_MIN_MAX_CLOSEST(pll_video0_clk, "pll-video0",
> >> +static SUNXI_CCU_NM_WITH_FRAC_GATE_LOCK_MIN_MAX_FEAT_NM_RATIO(pll_video0_clk,
> >> +						"pll-video0",
> >>  						"osc24M", 0x010,
> >>  						192000000,	/* Minimum rate */
> >>  						1008000000,	/* Maximum rate */
> 
> I just realized that adding the whole ratio limits for ccu_nm is
> superfluous as you could just as well express them in for of a minimum
> and maximum range:
> Since 8 <= N/M <= 25 and parent_rate = 24 MHz, therefore
>   192 MHz <= rate <= 600 MHz.

Good point!

> 
> These absolute limits are also listed in Allwinner's A64 manual.
> 
> BUT, here the upper limit was raised to 1008 MHz:
> 5de39acaf34604bd04834f092479cf4dcc946dd "clk: sunxi-ng: a64: Add max.
> rate constraint to video PLL"
> 
> With this upper limit the ratio limitation is effectively:
> 8 <= N/M <= 42
> 
> Icenowy Zheng (added to CC) had the reasonable explanation that this was
> used in the BSP kernel, so we should probably stick to that and ditch
> the two PLL-VIDEO0 related patches. What are your thoughts on that?

Ok, it seems that these patches are really superfluous. Remove them for v2.

Best regards,
Jernej

> 
> >> @@ -80,7 +81,10 @@ static SUNXI_CCU_NM_WITH_FRAC_GATE_LOCK_MIN_MAX_CLOSEST(pll_video0_clk, "pll-vid
> >>  						297000000,	/* frac rate 1 */
> >>  						BIT(31),	/* gate */
> >>  						BIT(28),	/* lock */
> >> -						CLK_SET_RATE_UNGATE);
> >> +						CLK_SET_RATE_UNGATE,
> >> +						CCU_FEATURE_FRACTIONAL |
> >> +						CCU_FEATURE_CLOSEST_RATE,
> >
> > Above flags are unrelated change, put them in new patch if needed.
> >
> > Best regards,
> > Jernej
> >
> >> +						8, 25);		/* min/max nm ratio */
> >>
> >>  static SUNXI_CCU_NM_WITH_FRAC_GATE_LOCK(pll_ve_clk, "pll-ve",
> >>  					"osc24M", 0x018,
> >>
> >>
>