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Date: Thu, 02 May 2024 17:55:01 +0000
Message-Id: <D0ZCO8KL5AQF.21Q70S27P7F5Z@folker-schwesinger.de>
Cc: "Chukun Pan" <amadeus@jmu.edu.cn>, "Heiko Stuebner" <heiko@sntech.de>,
 "Conor Dooley" <conor+dt@kernel.org>, "Krzysztof Kozlowski"
 <krzk+dt@kernel.org>, "Rob Herring" <robh@kernel.org>,
 <linux-arm-kernel@lists.infradead.org>,
 <linux-rockchip@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
 <devicetree@vger.kernel.org>
From: "Folker Schwesinger" <dev@folker-schwesinger.de>
To: "Dragan Simic" <dsimic@manjaro.org>, "Jonas Karlman" <jonas@kwiboo.se>
Subject: Re: [PATCH v2 2/2] arm64: dts: rockchip: Add Radxa ROCK 3C
References: <20240428123618.72170-1-amadeus@jmu.edu.cn>
 <20240428123618.72170-3-amadeus@jmu.edu.cn>
 <D0X7UJELGST3.2IL1AFDJ89N07@folker-schwesinger.de>
 <ded928414323ef4be51f2575d00ba7d1@manjaro.org>
 <832d6c37-a6c5-4468-9a23-1637b2affb90@kwiboo.se>
 <afa32c669ded2d37a4c11a54f1fc05b0@manjaro.org>
In-Reply-To: <afa32c669ded2d37a4c11a54f1fc05b0@manjaro.org>

Hi Jonas and Dragan,

On Thu May 2, 2024 at 3:48 PM CEST, Dragan Simic wrote:
> >>>> [...]
> >>>> +&sdhci {
> >>>> +	bus-width =3D <8>;
> >>>> +	max-frequency =3D <200000000>;
> >>>> +	mmc-hs200-1_8v;
> >>>=20
> >>> Out of curiosity, does this board also support HS400? From a very=20
> >>> brief
> >>> look this board seems quite similar to Rock 4 series boards, that do
> >>> support HS400.
> >>=20
> >> In a word, no, unfortunately.  In more detail, the Rockchip RK3566
> >> and RK3568 SoCs support the eMMC modes up to and including HS200, but
> >> not the HS400 mode.
> >=20
> > The datasheet for RK3568 only mention HS200 mode, however, HS400 mode=
=20
> > is
> > working in U-Boot after adjusting tap number for transmit clock [1].
> > Linux may need similar adjustment to make HS400 mode work on RK3568.
> >=20
> > RK3566 that this board use only support HS200, as specified in=20
> > datasheet.
>
> Oh, that's very interesting, thanks for pointing it out!
>
> What makes me a bit worried about enabling the undocumented HS400 mode
> on the RK3568 is that neither the RK3568 Hardware Design Guide (HDG),
> version 1.2, [2] mentions HS400 support.  I mean, the RK3568 datasheet
> may be wrong about not mentioning HS400, but what are the chances for
> the RK3568 HDG to also be wrong there?
>
> In other words, maybe there are some hard-to-trigger hardware issues
> in the RK3568 that made the HS400 mode, although actually present in
> hardware, officially unsupported for the RK3568?  Maybe there's even
> some non-public errata from Rockchip, who knows.
>
> [1]=20
> https://source.denx.de/u-boot/u-boot/-/commit/5c053f3adc69eaf83645b5d44c6=
adbb2d49a3fa7
> [2] https://dl.xkwy2018.com/downloads/RK3568/RK356X/Hardware/

Interesting indeed! Thanks to both of you for the info and for providing
links to the U-Boot commit and design guide. Much appreciated!