[PATCH] arm64: dts: rockchip: add enable-strobe-pulldown to emmc phy on rk3399

[Doug Anderson]

Hi,

On Tue, Aug 23, 2022 at 8:11 PM Jensen Huang
<jensenhuang at friendlyarm.com> wrote:
>
> Hi,
>
> Sorry for sending an email in HTML format.
>
> I realized that only some devices may be affected, so I considered
> modifying rk3399-nanopi4.dtsi only,
> but other boards without external pull-down should still need this patch.

I guess the other alternative would be to change how the dt property
works. You could say:

1. If `enable-strobe-pulldown` is set then enable the strobe pulldown.

2. If `enable-strobe-pulldown` is not set then don't touch the pin in
the kernel.

3. If someone later needs to explicitly disable the strobe pulldown
they could add a new property like `disable-strobe-pulldown`.


Obviously there are tradeoffs between that and what you've done and
I'm happy to let others make the call of which they'd prefer.


> BR,
> Jensen
>
> On Tue, Aug 23, 2022 at 10:13 PM Doug Anderson <dianders at chromium.org> wrote:
> >
> > Hi,
> >
> > On Tue, Aug 23, 2022 at 4:53 AM Heiko Stübner <heiko at sntech.de> wrote:
> > >
> > > Am Montag, 22. August 2022, 09:41:39 CEST schrieb Jensen Huang:
> > > > Internal pull-down for strobe line (GRF_EMMCPHY_CON2[9]) was disabled
> > > > by commit 8b5c2b45b8f0, which causes I/O error in HS400 mode.
> > > >
> > > > Tested on NanoPC-T4.
> > > >
> > > > Fixes: 8b5c2b45b8f0 ("phy: rockchip: set pulldown for strobe line in dts")
> > > > Signed-off-by: Jensen Huang <jensenhuang at friendlyarm.com>
> > >
> > > ok, so this looks like it restores previous functionality.
> > >
> > > I'm just wondering as the "offending" patch is from 2020, why this
> > > only turns up now. Any ideas?
> >
> > Ah, I see. So before the offending patch we used to just leave the
> > pull state at whatever the default was when the kernel was booted.
> > After the offending patch we chose a default.
> >
> > On kevin I see an external pull down on this line. Enabling both the
> > internal and external is probably not a huge deal, it'll just affect
> > the strength of the pull.
> >
> > On bob I _think_ the external pull down is also stuffed.
> >
> > ...so I guess that would explain why it didn't cause a problem for at
> > least those two boards?
> >
> > -Doug