Date: Thu, 27 Jun 2024 12:46:20 +0800
From: Chen-Yu Tsai <wens@...e.org>
To: "Pafford, Robert J." <pafford.9@...keyemail.osu.edu>
Cc: Frank Oltmanns <frank@...manns.dev>, Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...nel.org>, Jernej Skrabec <jernej.skrabec@...il.com>, 
	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-clk@...r.kernel.org>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, 
	"linux-sunxi@...ts.linux.dev" <linux-sunxi@...ts.linux.dev>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, 
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, 
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v4 1/5] clk: sunxi-ng: common: Support minimum and maximum rate

On Thu, Jun 27, 2024 at 9:23 AM Pafford, Robert J.
<pafford.9@...keyemail.osu.edu> wrote:
>
> Frank Oltmanns <frank@...manns.dev> writes:
>
> > Hi Robert,
> >
> > 26.06.2024 18:03:24 Pafford, Robert J. <pafford.9@...keyemail.osu.edu>:
> >
> >> Hi Frank,
> >>
> >> Moving to a new for loop makes sense. Let me know when you have a patch
> >
> > The patch is here, strange you didn't receive it:
> > https://lore.kernel.org/all/20240623-sunxi-ng_fix_common_probe-v1-1-7c97e32824a1@oltmanns.dev/
>
> Ah, this must have slipped through my inbox. I just applied it on my board and it is
> now cooperating with the min/max clock rates!

Please reply to the thread and give a Tested-by.

ChenYu

> >
> >> and I'll be glad to test it on my board. I do also wonder if this may
> >> have contributed to some of the HDMI issues seen in the other thread.
> >
> > My thought's exactly!
> >
> > Best regards,
> >   Frank
> >
> >>
> >> Best,
> >> Robert
> >>
> >>> Hi Robert,
> >>>
> >>> I'm truly sorry for the trouble the patch has caused you and for my late
> >>> reply!
> >>>
> >>> On 2024-06-14 at 23:52:08 +0000, "Pafford, Robert J." <pafford.9@...keyemail.osu.edu> wrote:
> >>>>> The Allwinner SoC's typically have an upper and lower limit for their
> >>>>> clocks' rates. Up until now, support for that has been implemented
> >>>>> separately for each clock type.
> >>>>>
> >>>>> Implement that functionality in the sunxi-ng's common part making use of
> >>>>> the CCF rate liming capabilities, so that it is available for all clock
> >>>>> types.
> >>>>>
> >>>>> Suggested-by: Maxime Ripard <mripard@...nel.org>
> >>>>> Signed-off-by: Frank Oltmanns <frank@...manns.dev>
> >>>>> Cc: stable@...r.kernel.org
> >>>>> ---
> >>>>>   drivers/clk/sunxi-ng/ccu_common.c | 19 +++++++++++++++++++
> >>>>>   drivers/clk/sunxi-ng/ccu_common.h |  3 +++
> >>>>>   2 files changed, 22 insertions(+)
> >>>>
> >>>> This patch appears to cause a buffer under-read bug due to the call to 'hw_to_ccu_common', which assumes all entries
> >>>> in the desc->hw_clocks->hws array are contained in ccu_common structs.
> >>>>
> >>>> However, not all clocks in the array are contained in ccu_common structs. For example, as part
> >>>> of the "sun20i-d1-ccu" driver, the "pll-video0" clock holds the 'clk_hw' struct inside of a 'clk_fixed_factor' struct,
> >>>> as it is a fixed factor clock based on the "pll-video0-4x" clock, created with the CLK_FIXED_FACTOR_HWS macro.
> >>>> This results in undefined behavior as the hw_to_ccu_common returns an invalid pointer referencing memory before the
> >>>> 'clk_fixed_factor' struct.
> >>>>
> >>>
> >>> Great catch! At first glance, it seems to me that calling
> >>> clk_hw_set_rate_range() in sunxi_ccu_probe() should not have happenend
> >>> in the loop that iterates over the hw_clks.
> >>>
> >>> Instead we should add one more loop that iterates over the ccu_clks.
> >>> Note, that there is already one such loop but, unfortunately, we can't
> >>> use that as it happens before the hw_clks loop and we can only call
> >>> clk_hw_set_rate_range() after the hw_clk has been registered.
> >>>
> >>> Hence, I propose to move the offending code to a new loop:
> >>>         for (i = 0; i < desc->num_ccu_clks; i++) {
> >>>                 struct ccu_common *cclk = desc->ccu_clks[i];
> >>>
> >>>                 if (!cclk)
> >>>                         continue;
> >>>
> >>>                 if (cclk->max_rate)
> >>>                         clk_hw_set_rate_range(&cclk->hw, common->min_rate,
> >>>                                               common->max_rate);
> >>>                 else
> >>>                         WARN(cclk->min_rate,
> >>>                              "No max_rate, ignoring min_rate of clock %d - %s\n",
> >>>                              i, cclk->hw.init->name);
> >>>         }
> >>>
> >>> I haven't tested (or even compiled) the above, but I'll test and send a
> >>> patch within the next few days for you to test.
> >>>
> >>> Thanks again,
> >>>   Frank
> >>>
> >>>>
> >>>> I have attached kernel warnings from a system based on the "sun8i-t113s.dtsi" device tree, where the memory contains
> >>>> a non-zero value for the min-rate but a zero value for the max-rate, triggering the "No max_rate, ignoring min_rate"
> >>>> warning in the 'sunxi_ccu_probe' function.
> >>>>
> >>>> [...]
>
> Thanks,
> Robert

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