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Message-ID: <871f0b24a38208d9c5d6abc87d83b067162c103e.camel@gmail.com>
Subject: Re: [PATCH 1/3] phy: rockchip: emmc: Enable pulldown for strobe line
From: Alban Browaeys <alban.browaeys@gmail.com>
To: Conor Dooley <conor@kernel.org>, dev@folker-schwesinger.de
Cc: Vinod Koul <vkoul@kernel.org>, Kishon Vijay Abraham I
 <kishon@kernel.org>,  Heiko Stuebner <heiko@sntech.de>, Chris Ruehl
 <chris.ruehl@gtsys.com.hk>, Rob Herring <robh@kernel.org>, Krzysztof
 Kozlowski <krzysztof.kozlowski+dt@linaro.org>,  Conor Dooley
 <conor+dt@kernel.org>, Christopher Obbard <chris.obbard@collabora.com>,
 Doug Anderson <dianders@chromium.org>, Brian Norris
 <briannorris@chromium.org>, Jensen Huang <jensenhuang@friendlyarm.com>,
 linux-phy@lists.infradead.org,  linux-arm-kernel@lists.infradead.org,
 linux-rockchip@lists.infradead.org,  linux-kernel@vger.kernel.org,
 devicetree@vger.kernel.org
Date: Thu, 28 Mar 2024 18:00:03 +0100
In-Reply-To: <20240326-tactical-onlooker-3df8d2352dc2@spud>
References: 
	<20240326-rk-default-enable-strobe-pulldown-v1-0-f410c71605c0@folker-schwesinger.de>
	 <20240326-rk-default-enable-strobe-pulldown-v1-1-f410c71605c0@folker-schwesinger.de>
	 <20240326-tactical-onlooker-3df8d2352dc2@spud>
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Le mardi 26 mars 2024 =C3=A0 19:46 +0000, Conor Dooley a =C3=A9crit=C2=A0:
> On Tue, Mar 26, 2024 at 07:54:35PM +0100, Folker Schwesinger via B4
> Relay wrote:
> > From: Folker Schwesinger <dev@folker-schwesinger.de>
> > -	if (of_property_read_bool(dev->of_node, "rockchip,enable-
> > strobe-pulldown"))
> > -		rk_phy->enable_strobe_pulldown =3D
> > PHYCTRL_REN_STRB_ENABLE;
> > +	if (of_property_read_bool(dev->of_node, "rockchip,disable-
> > strobe-pulldown"))
> > +		rk_phy->enable_strobe_pulldown =3D
> > PHYCTRL_REN_STRB_DISABLE;
>=20
> Unfortunately you cannot do this.
> Previously no property at all meant disabled and a property was
> required
> to enable it. With this change the absence of a property means that
> it
> will be enabled.
> An old devicetree is that wanted this to be disabled would have no
> property and will now end up with it enabled. This is an ABI break
> and is
> clearly not backwards compatible, that's a NAK unless it is
> demonstrable
> that noone actually wants to disable it at all.


But the patch that introduced the new default to disable the pulldown
explicitely introduced a regression for at least 4 boards.
It took time to sort out that the default to disable pulldown was the
culprit but still.
Will we carry this new behavor that breaks the default design for
rk3399 because since the regression was introduced new board definition
might have expceted this new behavior.

Could the best option be to revert to =C3=A9not set a default enable/disabl=
e
pulldown" (as before the commit that introduced the regression) and
allow one to force the pulldown via the enable/disable pulldown
property?
I mean the commit that introduced a default value for the pulldown did
not seem to be about fixing anything. But it broke a lot. ANd it was
really really hard to find the description of this commit to understand
that one had to enable pulldown to restore hs400.

In more than 3 years, only one board maintainer noticed that this
property was required to get back HS400  and thanks to a user telling
me that this board was working I found from this board that this
property was "missing" from most board definitions (while it was not
required before).


I am all for not breaking ABI. But what about not reverting a patch
that already broke ABI because this patch introduced a new ABI that we
don't want to break?
I mean shouldn't a new commit with a new ABI that regressed the kernel
be reverted?

Mind fixing the initial regression 8b5c2b45b8f0 "phy: rockchip: set
pulldown for strobe line in dts" does not necessarily mean changing the
default to the opposite value but could also be reverting to not
setting a default.
Though I don't know if there are pros to setting a default.


> If this patch fixes a problem on a board that you have, I would
> suggest
> that you add the property to enable it, as the binding tells you to.
>=20
> Thanks,
> Conor.


Regards,
Alban