Re: [PATCH v3 4/7] arm64: dts: allwinner: a64: reset pll-video0 rate

From: Frank Oltmanns <frank@oltmanns.dev>
To: "Jernej Škrabec" <jernej.skrabec@gmail.com>
Cc: Maxime Ripard <mripard@kernel.org>, Chen-Yu Tsai <wens@csie.org>,
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
	Samuel Holland <samuel@sholland.org>, Roman Beranek <me@crly.cz>,
	Icenowy Zheng <icenowy@aosc.io>, Ondrej Jirman <megi@xff.cz>,
	dri-devel@lists.freedesktop.org,
	linux-arm-kernel@lists.infradead.org,
	linux-sunxi@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 4/7] arm64: dts: allwinner: a64: reset pll-video0 rate
Date: Sat, 29 Apr 2023 20:28:38 +0200	[thread overview]
Message-ID: <87wn1uleje.fsf@oltmanns.dev> (raw)
In-Reply-To: <4477541.LvFx2qVVIh@jernej-laptop>

Hi Jernej,

On 2023-04-28 at 08:43:29 +0200, Jernej Škrabec <jernej.skrabec@gmail.com> wrote:
> Dne četrtek, 27. april 2023 ob 11:16:08 CEST je Roman Beranek napisal(a):
>> With pll-mipi as its source clock, the exact rate to which TCON0's data
>> clock can be set to is constrained by the current rate of pll-video0.
>> Unless changed on a request of another consumer, the rate of pll-video0
>> is left as inherited from the bootloader.
>>
>> The default rate on reset is 297 MHz, a value preferable to what it is
>> later set to in u-boot (294 MHz). This happens unintentionally though,
>> as u-boot, for the sake of simplicity, rounds the rate requested by DE2
>> driver (297 MHz) to 6 MHz steps.
>>
>> Reset the PLL to its default rate of 297 MHz.
>
> Why would that be preferable? You actually dropped "clk: sunxi-ng: a64:
> propagate rate change from pll-mipi" patch which would take care for adjusting
> parent rate to correct value.

For me, on the pinephone, it somehow doesn't. Please see here:
https://lore.kernel.org/all/87cz3uzpx1.fsf@oltmanns.dev/

I haven't figured out yet why that is. But hopefully, I'll find time in
the coming days / weeks to look into that.

Best regards,
  Frank

> Best regards,
> Jernej
>
>>
>> Signed-off-by: Roman Beranek <me@crly.cz>
>> ---
>>  arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
>> b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi index
>> e6a194db420d..cfc60dce80b0 100644
>> --- a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
>> +++ b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
>> @@ -667,6 +667,9 @@ ccu: clock@1c20000 {
>>  			clock-names = "hosc", "losc";
>>  			#clock-cells = <1>;
>>  			#reset-cells = <1>;
>> +
>> +			assigned-clocks = <&ccu CLK_PLL_VIDEO0>;
>> +			assigned-clock-rates = <297000000>;
>>  		};
>>
>>  		pio: pinctrl@1c20800 {

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