linux-kernel - Re: [PATCH 3/4] phy: rockchip-typec: support DP phy switch

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Message-ID: <1626236.28xlsfuSeg@diego>
Date:   Thu, 09 Mar 2017 09:31:33 +0100
From:   Heiko Stübner <heiko@...ech.de>
To:     Brian Norris <briannorris@...omium.org>
Cc:     Chris Zhong <zyw@...k-chips.com>, dri-devel@...ts.freedesktop.org,
        kishon@...com, robh@...nel.org, linux-rockchip@...ts.infradead.org,
        linux-kernel@...r.kernel.org, seanpaul@...omium.org,
        groeck@...omium.org, linux-arm-kernel@...ts.infradead.org,
        mark.yao@...k-chips.com, Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH 3/4] phy: rockchip-typec: support DP phy switch

Hi Brian,

Am Mittwoch, 8. März 2017, 19:10:50 CET schrieb Brian Norris:
> On Thu, Mar 09, 2017 at 02:02:54AM +0100, Heiko Stuebner wrote:
> > Am Mittwoch, 8. März 2017, 16:39:23 CET schrieb Brian Norris:
> > > On Fri, Feb 10, 2017 at 03:44:13PM +0800, Chris Zhong wrote:
> > > > There are 2 Type-c PHYs in RK3399, but only one DP controller. Hence
> > > > only one PHY can connect to DP controller at one time, the other
> > > > should
> > > > be disconnected. The GRF_SOC_CON26 register has a switch bit to do it,
> > > > set this bit means enable PHY 1, clear this bit means enable PHY 0.
> > > > 
> > > > Signed-off-by: Chris Zhong <zyw@...k-chips.com>
> > > > ---
> > > > 
> > > >  drivers/phy/phy-rockchip-typec.c | 9 +++++++++
> > > >  1 file changed, 9 insertions(+)
> > > > 
> > > > diff --git a/drivers/phy/phy-rockchip-typec.c
> > > > b/drivers/phy/phy-rockchip-typec.c index 7cfb0f8..1604aaa 100644
> > > > --- a/drivers/phy/phy-rockchip-typec.c
> > > > +++ b/drivers/phy/phy-rockchip-typec.c
> 
> ...
> 
> > > > @@ -869,6 +873,11 @@ static int tcphy_parse_dt(struct
> > > > rockchip_typec_phy
> > > > *tcphy,>
> > > > 
> > > >  	if (ret)
> > > >  	
> > > >  		return ret;
> > > > 
> > > > +	ret = tcphy_get_param(dev, &cfg->uphy_dp_sel,
> > > > +			      "rockchip,uphy-dp-sel");
> > > > +	if (ret)
> > > > +		return ret;
> > > 
> > > What about existing device trees? You're essentially adding this
> > > new property and requiring it at the same time.
> > > 
> > > Or are we considering no RK3399 DP stable at the moment? I guess we
> > > haven't actually merged any device trees that support this yet, no?
> > 
> > An interesting situation we're in here. On the one hand, you're right this
> > breaks "backwards compatiblity".
> > 
> > But on the other hand, the type-c phy is currently very much unused. The
> > only current board rk3399-evb.dts does not enable them (so they're
> > disabled everywhere) and we have neither dwc3 nor dp nodes in any rk3399
> > devicetrees so far. Also Rob was ok with the binding change :-) .
> > 
> > So from my pov, I'd say it _should_ be ok, as nothing is using the phys at
> > all yet and thus there is nothing that could get broken.
> 
> Yeah, I guess it's OK... but BTW out-of-tree DTs are perfectly
> legit, once the bindings are accepted.
> 
> Another random point of contention (not worth too much, as the pattern
> is already set), but why do these deserve DT properties at all? The
> device already has a "rk3399" compatible property, so can't we derive
> GRF offsets from that?

I'm definitly with you in this regard.

But it seems like there is some sort of current trend of moving more stuff 
into the dt again. I vaguely remember phy and (or) dt-maintainers preferring 
to have these definitions in the dt for the typec-phy.

See also the recent mail from Olof concerning the grf initialization and maybe 
not having per-soc definitions in the driver, where I'm trying to keep things 
out of the dt a bit more strongly :-) .

So yes, personally I would definitly prefer not having to much GRF-stuff leak 
into the dt. Simply because the GRF has always been very unstable over time 
[=you always find one more bit that needs tuning] and to not cause things like 
the above. But as you said I guess we're to late for the typec-phy.


Heiko