Message-ID: <3546609.iIbC2pHGDl@jernej-laptop>
Date: Mon, 26 Feb 2024 18:29:28 +0100
From: Jernej Škrabec <jernej.skrabec@...il.com>
To: Ondřej Jirman <megi@....cz>,
 Maxime Ripard <mripard@...nel.org>, 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>,
 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 0/6] Pinephone video out fixes (flipping between two frames)

Dne ponedeljek, 26. februar 2024 ob 08:13:42 CET je Frank Oltmanns napisal(a):
> Hi Jernej,
> hi Maxime,
> hi Ondřej,
> 
> On 2024-02-19 at 10:41:19 +0100, Frank Oltmanns <frank@...manns.dev> wrote:
> > Hi Ondřej,
> >
> > On 2024-02-11 at 20:25:29 +0100, Ondřej Jirman <megi@....cz> wrote:
> >> Hi Frank,
> >>
> >> On Sun, Feb 11, 2024 at 04:09:16PM +0100, Frank Oltmanns wrote:
> >>> Hi Ondřej,
> >>>
> >>> On 2024-02-05 at 17:02:00 +0100, Ondřej Jirman <megi@....cz> wrote:
> >>> > On Mon, Feb 05, 2024 at 04:54:07PM +0100, Ondřej Jirman wrote:
> >>> >> On Mon, Feb 05, 2024 at 04:22:23PM +0100, Frank Oltmanns wrote:
> >>> >>
> >>> >> [...]
> >>> >>
> >>> >> Also sunxi-ng clk driver does apply NM factors at once to PLL_GPU clock,
> >>> >> which can cause sudden frequency increase beyond intended output frequency,
> >>> >> because division is applied immediately while multiplication is reflected
> >>> >> slowly.
> >>> >>
> >>> >> Eg. if you're changing divider from 7 to 1, you can get a sudden 7x output
> >>> >> frequency spike, before PLL VCO manages to lower the frequency through N clk
> >>> >> divider feedback loop and lock on again. This can mess up whatever's connected
> >>> >> to the output quite badly.
> >>> >>
> >>> >> You'd have to put logging on kernel writes to PLL_GPU register to see what
> >>> >> is written in there and if divider is lowered significantly on some GPU
> >>> >> devfreq frequency transitions.
> >>>
> >>> By looking at the clocks in clk_summary in debugfs, the rate of PLL-GPU
> >>> always matches the rate of the GPU (at least at 120, 312, and 432 MHz).
> >>> This is further underlined by the fact, that none of the rates can be
> >>> achieved by integer dividing one of the other rates. sunxi-ng would
> >>> only favor a different rate for pll-gpu than the one that is requested
> >>> for the gpu, if pll-gpu is already running at a rate such that there
> >>> exists an M ∈ {1, 2, 3, 4, 5, 6, 7, 8}, where
> >>>   rate of pll-gpu / M = requested gpu rate
> >>> or if the requested rate could not be reached directly by pll-gpu. Both
> >>> is not the case for the rates in question (120, 192, 312, and 432 MHz).
> >>>
> >>> This means that the following divisor/multipliers are used by sunxi-ng's
> >>> ccu_nm:
> >>> N =  5, M = 1 for 120 MHz (min value without PATCH 6)
> >>> N =  8, M = 1 for 192 MHz (min value after applying PATCH 6)
> >>> N = 13, M = 1 for 312 MHz
> >>> N = 18, M = 1 for 432 MHz
> >>>
> >>> So, with or without PATCH 6, the divider stays constant and it's only
> >>> the multiplier that changes. This means, there should be no unexpected
> >>> frequency spikes, right?
> >>
> >> Maybe. Thanks for giving it a try. There may still be other kinds of glitches
> >> even if the divisor stays the same. It all depends how the register update is
> >> implemented in the PLL block. It's hard to say. I guess, unless Allwinner
> >> guarantees glitchless output from a given PLL when changing its parameters,
> >> you can't rely on the output being clean during changes.
> >>
> >>> >> It's also unclear what happens when FRAC_CLK_OUT or PLL_MODE_SEL changes.
> >>>
> >>> Those are not changed once the clock is initialized. The bug however
> >>> occurs hours or days after booting. IMO, this makes it unlikely that this
> >>> could be the culprit.
> >>>
> >>> >> Maybe not much because M is supposed to be set to 1, but you still need to
> >>> >> care when enabling fractional mode, and setting M to 1 because that's exactly
> >>> >> the bad scenario if M was previously higher than 1.
> >>> >>
> >>> >> It's tricky.
> >>> >>
> >>> >> Having GPU module clock gated during PLL config changes may help! You can
> >>> >> do that without locking yourself out, unlike with the CPU PLL.
> >>> >>
> >>> >> There's a gate enable bit for it at GPU_CLK_REG.SCLK_GATING. (page 122)
> >>>
> >>> The GPU should already be properly gated:
> >>> https://elixir.bootlin.com/linux/v6.7.4/source/drivers/clk/sunxi-ng/ccu-sun50i-a64.c#L599
> >>
> >> How so? That's just clock declaration. How does it guarantee the clock to the
> >> module is gated during parent PLL configuration changes?
> >>
> >
> > You're of course right.
> >
> > I now tried using a similar approach like the one for changes for on
> > PLL-CPU. It's using a notifier to connect the CPU to the 24 MHz
> > oscillator and, after PLL-CPU is at its new rate, connecting it back to
> > PLL-CPU.
> >
> > For the GPU my approach was to disable the GPU prior to changing
> > PLL-GPU's rate and then re-enabling it, once the rate change is
> > complete. I think, that's what you were proposing, right?
> >
> > Unfortunately, this results in a frozen phone even more quickly.
> >
> > Below is my code. Again, it doesn't solve the problem, but maybe
> > somebody can spot what I'm doing wrong.
> 
> It seems to me that all options for changing the GPU's rate in a stable
> manner have been exhausted. There seems to be no common interpretation
> what the phrase "Clock output of PLL_GPU can be used for GPU;and dynamic
> frequency scaling is not supported" in the Allwinner A64 manual (chapter
> 3.3.3) means.
> 
> The BSP uses a fixed rate of 432 MHz. Unless one of you has a clever
> idea, I suggest to remove the OPPs from the device tree and set the GPU
> to 432 MHz.
> 
> What are your thoughts on that?

I can't find original source of these points. So I'm good with removing
them. But instead of fully removing table, you can just leave one point and
it should work.

Best regards,
Jernej

> 
> Best regards,
>   Frank
> 
> >
> > Best regards,
> >   Frank
> >
> > diff --git a/drivers/clk/sunxi-ng/ccu-sun50i-a64.c b/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
> > index d68bdf7dd342..74538259d67a 100644
> > --- a/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
> > +++ b/drivers/clk/sunxi-ng/ccu-sun50i-a64.c
> > @@ -977,6 +977,11 @@ static struct ccu_rate_reset_nb sun50i_a64_pll_video0_reset_tcon0_nb = {
> >
> >  #define CCU_MIPI_DSI_CLK 0x168
> >
> > +static struct ccu_div_nb sun50i_a64_gpu_nb = {
> > +	.common		= &gpu_clk.common,
> > +	.delay_us	= 1, /* ??? */
> > +};
> > +
> >  static int sun50i_a64_ccu_probe(struct platform_device *pdev)
> >  {
> >  	void __iomem *reg;
> > @@ -1025,6 +1030,10 @@ static int sun50i_a64_ccu_probe(struct platform_device *pdev)
> >  	sun50i_a64_pll_video0_reset_tcon0_nb.target_clk = tcon0_clk.common.hw.clk;
> >  	ccu_rate_reset_notifier_register(&sun50i_a64_pll_video0_reset_tcon0_nb);
> >
> > +	/* Gate then ungate GPU on PLL-GPU changes */
> > +	ccu_div_notifier_register(pll_gpu_clk.common.hw.clk,
> > +				  &sun50i_a64_gpu_nb);
> > +
> >  	return 0;
> >  }
> >
> > diff --git a/drivers/clk/sunxi-ng/ccu_div.c b/drivers/clk/sunxi-ng/ccu_div.c
> > index cb10a3ea23f9..83813c54fb2f 100644
> > --- a/drivers/clk/sunxi-ng/ccu_div.c
> > +++ b/drivers/clk/sunxi-ng/ccu_div.c
> > @@ -4,7 +4,9 @@
> >   * Maxime Ripard <maxime.ripard@...e-electrons.com>
> >   */
> >
> > +#include <linux/clk.h>
> >  #include <linux/clk-provider.h>
> > +#include <linux/delay.h>
> >  #include <linux/io.h>
> >
> >  #include "ccu_gate.h"
> > @@ -142,3 +144,37 @@ const struct clk_ops ccu_div_ops = {
> >  	.set_rate	= ccu_div_set_rate,
> >  };
> >  EXPORT_SYMBOL_NS_GPL(ccu_div_ops, SUNXI_CCU);
> > +
> > +static int ccu_div_notifier_cb(struct notifier_block *nb,
> > +			       unsigned long event, void *data)
> > +{
> > +	struct ccu_div_nb *div_nb = to_ccu_div_nb(nb);
> > +
> > +	if (event == PRE_RATE_CHANGE) {
> > +		div_nb->original_enable = ccu_div_is_enabled(&div_nb->common->hw);
> > +		if (div_nb->original_enable) {
> > +			ccu_div_disable(&div_nb->common->hw);
> > +			udelay(div_nb->delay_us);
> > +		}
> > +	} else if (event == POST_RATE_CHANGE) {
> > +		if (div_nb->original_enable) {
> > +			ccu_div_enable(&div_nb->common->hw);
> > +			udelay(div_nb->delay_us);
> > +		}
> > +	}
> > +
> > +	return NOTIFY_OK;
> > +}
> > +
> > +int ccu_div_notifier_register(struct clk *clk, struct ccu_div_nb *div_nb)
> > +{
> > +	div_nb->clk_nb.notifier_call = ccu_div_notifier_cb;
> > +
> > +	return clk_notifier_register(clk, &div_nb->clk_nb);
> > +}
> > diff --git a/drivers/clk/sunxi-ng/ccu_div.h b/drivers/clk/sunxi-ng/ccu_div.h
> > index 90d49ee8e0cc..e096c7be5dca 100644
> > --- a/drivers/clk/sunxi-ng/ccu_div.h
> > +++ b/drivers/clk/sunxi-ng/ccu_div.h
> > @@ -283,4 +283,16 @@ static inline struct ccu_div *hw_to_ccu_div(struct clk_hw *hw)
> >
> >  extern const struct clk_ops ccu_div_ops;
> >
> > +struct ccu_div_nb {
> > +	struct notifier_block	clk_nb;
> > +	struct ccu_common	*common;
> > +
> > +	u32	delay_us;	/* us to wait after changing parent rate */
> > +	int	original_enable;/* This is set by the notifier callback */
> > +};
> > +
> > +#define to_ccu_div_nb(_nb) container_of(_nb, struct ccu_div_nb, clk_nb)
> > +
> > +int ccu_div_notifier_register(struct clk *clk, struct ccu_div_nb *mux_nb);
> > +
> >  #endif /* _CCU_DIV_H_ */
> >
> >
> >
> >>
> >> CLK_SET_RATE_PARENT only gates output on re-parenting, not on parent rate changes,
> >> according to the header:
> >>
> >>   https://elixir.bootlin.com/linux/v6.7.4/source/include/linux/clk-provider.h#L19
> >>
> >> You'd need perhaps CLK_SET_RATE_GATE *and* still verify that it actually works
> >> as expected via some tracing of gpu clock enable/disable/set_rate and pll-gpu
> >> set_rate. CLK_SET_RATE_GATE seems confusingly docummented:
> >>
> >>   https://elixir.bootlin.com/linux/v6.7.4/source/drivers/clk/clk.c#L1034
> >>
> >> so I don't particularly trust it does exaclty what the header claims and what
> >> would be needed to test the theory that gating gpu clock during rate change
> >> might help.
> >>
> >> kind regards,
> >> 	o.
> >>
> >>> Thank you for your detailed proposal! It was insightful to read. But
> >>> while those were all great ideas, they have all already been taken care
> >>> of. I'm fresh out of ideas again (except for pinning the GPU rate).
> >>>
> >>> Again, thank you so much,
> >>>   Frank
> >>>
> >>> >>
> >>> >> Kind regards,
> >>> >> 	o.
> >>> >>
> >>> >> > I very much appreciate your feedback!
> >>> >> >
> >>> >> > [1] https://gitlab.com/postmarketOS/pmaports/-/issues/805
> >>> >> >
> >>> >> > Signed-off-by: Frank Oltmanns <frank@...manns.dev>
> >>> >> > ---
> >>> >> > Changes in v2:
> >>> >> > - dts: Increase minimum GPU frequency to 192 MHz.
> >>> >> > - nkm and a64: Add minimum and maximum rate for PLL-MIPI.
> >>> >> > - nkm: Use the same approach for skipping invalid rates in
> >>> >> >   ccu_nkm_find_best() as in ccu_nkm_find_best_with_parent_adj().
> >>> >> > - nkm: Improve names for ratio struct members and hence get rid of
> >>> >> >   describing comments.
> >>> >> > - nkm and a64: Correct description in the commit messages: M/N <= 3
> >>> >> > - Remove patches for nm as they were not needed.
> >>> >> > - st7703: Rework the commit message to cover more background for the
> >>> >> >   change.
> >>> >> > - Link to v1: https://lore.kernel.org/r/20231218-pinephone-pll-fixes-v1-0-e238b6ed6dc1@oltmanns.dev
> >>> >> >
> >>> >> > ---
> >>> >> > Frank Oltmanns (6):
> >>> >> >       clk: sunxi-ng: nkm: Support constraints on m/n ratio and parent rate
> >>> >> >       clk: sunxi-ng: a64: Add constraints on PLL-MIPI's n/m ratio and parent rate
> >>> >> >       clk: sunxi-ng: nkm: Support minimum and maximum rate
> >>> >> >       clk: sunxi-ng: a64: Set minimum and maximum rate for PLL-MIPI
> >>> >> >       drm/panel: st7703: Drive XBD599 panel at higher clock rate
> >>> >> >       arm64: dts: allwinner: a64: Fix minimum GPU OPP rate
> >>> >> >
> >>> >> >  arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi |  4 ++--
> >>> >> >  drivers/clk/sunxi-ng/ccu-sun50i-a64.c         | 14 +++++++----
> >>> >> >  drivers/clk/sunxi-ng/ccu_nkm.c                | 34 +++++++++++++++++++++++++++
> >>> >> >  drivers/clk/sunxi-ng/ccu_nkm.h                |  4 ++++
> >>> >> >  drivers/gpu/drm/panel/panel-sitronix-st7703.c | 14 +++++------
> >>> >> >  5 files changed, 56 insertions(+), 14 deletions(-)
> >>> >> > ---
> >>> >> > base-commit: 059c53e877ca6e723e10490c27c1487a63e66efe
> >>> >> > change-id: 20231218-pinephone-pll-fixes-0ccdfde273e4
> >>> >> >
> >>> >> > Best regards,
> >>> >> > --
> >>> >> > Frank Oltmanns <frank@...manns.dev>
> >>> >> >
> 

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