linux-kernel - Re: [PATCH 1/3] phy: rockchip: emmc: Enable pulldown for strobe line

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Message-Id: <D04O57YQHYI4.1QNGSVKVT44CS@folker-schwesinger.de>
Date: Wed, 27 Mar 2024 16:21:45 +0000
From: "Folker Schwesinger" <dev@...ker-schwesinger.de>
To: "Dragan Simic" <dsimic@...jaro.org>, "Conor Dooley" <conor@...nel.org>
Cc: "Vinod Koul" <vkoul@...nel.org>, "Kishon Vijay Abraham I"
 <kishon@...nel.org>, "Heiko Stuebner" <heiko@...ech.de>, "Chris Ruehl"
 <chris.ruehl@...ys.com.hk>, "Rob Herring" <robh@...nel.org>, "Krzysztof
 Kozlowski" <krzysztof.kozlowski+dt@...aro.org>, "Conor Dooley"
 <conor+dt@...nel.org>, "Christopher Obbard" <chris.obbard@...labora.com>,
 "Alban Browaeys" <alban.browaeys@...il.com>, "Doug Anderson"
 <dianders@...omium.org>, "Brian Norris" <briannorris@...omium.org>, "Jensen
 Huang" <jensenhuang@...endlyarm.com>, <linux-phy@...ts.infradead.org>,
 <linux-arm-kernel@...ts.infradead.org>,
 <linux-rockchip@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
 <devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/3] phy: rockchip: emmc: Enable pulldown for strobe
 line

Hi Conor and Dragan,

thanks for your feedback!

On Tue Mar 26, 2024 at 8:55 PM CET, Dragan Simic wrote:
> On 2024-03-26 20:46, Conor Dooley wrote:
> > On Tue, Mar 26, 2024 at 07:54:35PM +0100, Folker Schwesinger via B4
> > Relay wrote:
> >> From: Folker Schwesinger <dev@...ker-schwesinger.de>
> >>
> >> Restore the behavior of the Rockchip kernel that undconditionally
> >> enables the internal strobe pulldown.
> >
> > What do you mean "restore the behaviour of the rockchip kernel"? Did
> > mainline behave the same as the rockchip kernel previously? If not,
> > using "restore" here is misleading. "Unconditionally" is also
> > incorrect,
> > because you have a property that disables it.

Apologizes for the misleading commit message. Prior to 5.11 the Linux
kernel did not touch the pull-down registers. However, it seems the
register's (factory?) default was set to enable the pull-down. As it
was mentioned elsewhere that was the configuration recommended by
Rockchip. The 4.4 vendor (Rockchip) kernel reflects that by enabling the
pull-down in its kernel.
Of course, this has nothing to do with the Linux kernel, so "restore"
was a bad choice here.

I previously had split the driver patch into two separate patches, one
for changing the default (unconditionally at that point), the other for
adding the disable property. As both changes were minimal I decided to
squash the commits. I updated the cover letter, but forgot to update the
commit message. Sorry.

> >> Fixes: 8b5c2b45b8f0 ("phy: rockchip: set pulldown for strobe line in
> >> dts")
> >> Signed-off-by: Folker Schwesinger <dev@...ker-schwesinger.de>
> >> ---
> >>  drivers/phy/rockchip/phy-rockchip-emmc.c | 6 +++---
> >>  1 file changed, 3 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/phy/rockchip/phy-rockchip-emmc.c
> >> b/drivers/phy/rockchip/phy-rockchip-emmc.c
> >> index 20023f6eb994..6e637f3e1b19 100644
> >> --- a/drivers/phy/rockchip/phy-rockchip-emmc.c
> >> +++ b/drivers/phy/rockchip/phy-rockchip-emmc.c
> >> @@ -376,14 +376,14 @@ static int rockchip_emmc_phy_probe(struct
> >> platform_device *pdev)
> >>  	rk_phy->reg_offset = reg_offset;
> >>  	rk_phy->reg_base = grf;
> >>  	rk_phy->drive_impedance = PHYCTRL_DR_50OHM;
> >> -	rk_phy->enable_strobe_pulldown = PHYCTRL_REN_STRB_DISABLE;
> >> +	rk_phy->enable_strobe_pulldown = PHYCTRL_REN_STRB_ENABLE;
> >>  	rk_phy->output_tapdelay_select = PHYCTRL_OTAPDLYSEL_DEFAULT;
> >>
> >>  	if (!of_property_read_u32(dev->of_node, "drive-impedance-ohm",
> >> &val))
> >>  		rk_phy->drive_impedance = convert_drive_impedance_ohm(pdev, val);
> >>
> >> -	if (of_property_read_bool(dev->of_node,
> >> "rockchip,enable-strobe-pulldown"))
> >> -		rk_phy->enable_strobe_pulldown = PHYCTRL_REN_STRB_ENABLE;
> >> +	if (of_property_read_bool(dev->of_node,
> >> "rockchip,disable-strobe-pulldown"))
> >> +		rk_phy->enable_strobe_pulldown = PHYCTRL_REN_STRB_DISABLE;
> >
> > 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.
> >
>
> Moreover, as I already explained some time ago, [1] some boards and
> devices are unfortunately miswired, and we don't want to enable the
> DATA STROBE pull-down on such boards.
>
> [1]
> https://lore.kernel.org/linux-rockchip/ca5b7cad01f645c7c559ab26a8db8085@manjaro.org/#t
>
> > 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.

I agree, I'll post the patches later.

Best regards

Folker


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