Re: [PATCH 0/4] Move DP phy switch to PHY driver

From: "Heiko Stübner" <heiko@sntech.de>
To: Doug Anderson <dianders@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	David Airlie <airlied@linux.ie>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Shawn Lin <shawn.lin@rock-chips.com>,
	Will Deacon <will.deacon@arm.com>,
	Kever Yang <kever.yang@rock-chips.com>,
	dri-devel@lists.freedesktop.org,
	Guenter Roeck <groeck@chromium.org>,
	Chris Zhong <zyw@rock-chips.com>,
	Brian Norris <briannorris@chromium.org>,
	Kishon Vijay Abraham I <kishon@ti.com>,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>,
	Jianqun Xu <jay.xu@rock-chips.com>,
	Caesar Wang <wxt@rock-chips.com>,
	devicetree@vger.kernel.org,
	Elaine Zhang <zhangqing@rock-chips.com>,
	Rob Herring <robh+dt@kernel.org>,
	William wu <wulf@rock-chips.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Tomasz Figa <tfiga@chromium.org>,
	David Wu <david.wu@rock-chips.com>,
	Enric Balletbo i Serra <enric.balletb>
Subject: Re: [PATCH 0/4] Move DP phy switch to PHY driver
Date: Mon, 04 Dec 2017 22:53:03 +0100	[thread overview]
Message-ID: <4518665.CiImf8ftzB@diego> (raw)
In-Reply-To: <CAD=FV=XVCCbh6P-WweccyKiNy2RJRhqY-6gpf7BVkY4oqdDZbg@mail.gmail.com>

Hi,

Am Montag, 4. Dezember 2017, 08:08:31 CET schrieb Doug Anderson:
> On Sun, Dec 3, 2017 at 11:46 PM, Heiko Stübner <heiko@sntech.de> wrote:
> > Am Montag, 4. Dezember 2017, 10:47:08 CET schrieb Chris Zhong:
> >> On 2017年12月02日 05:58, Heiko Stuebner wrote:
> >> > Am Freitag, 1. Dezember 2017, 13:42:46 CET schrieb Doug Anderson:
> >> >> On Wed, Nov 29, 2017 at 6:27 PM, Chris Zhong <zyw@rock-chips.com> 
wrote:
> >> >>> Thank you for mentioning this patch.
> >> >>> 
> >> >>> I think the focus of the discussion is: can we put the grf control
> >> >>> bit
> >> >>> to
> >> >>> dts.
> >> >>> 
> >> >>> The RK3399 has 2 Type-C phy, but only one DP controller, this
> >> >>> "uphy_dp_sel"
> >> >>> 
> >> >>> can help to switch these 2 phy. So I think this bit can be considered
> >> >>> as
> >> >>> a
> >> >>> part of
> >> >>> 
> >> >>> Type-C phy, these 2 phy have different bits, just similar to other
> >> >>> bits
> >> >>> (such as "pipe-status").
> >> >>> 
> >> >>> Put them to DTS file might be a accepted practice.
> >> >> 
> >> >> I guess the first step would be finding the person to make a decision.
> >> >> Is that Heiko?  Olof?  Kishon?  Rob?.  As I see it there are a few
> >> >> options:
> >> >> 
> >> >> 1. Land this series as-is.  This makes the new bit work just like all
> >> >> the other ones next to it.  If anyone happens to try to use an old
> >> >> device tree on a new kernel they'll break.  Seems rather unlikely
> >> >> given that the whole type C PHY is not really fully functional
> >> >> upstream, but technically this is a no-no from a device tree
> >> >> perspective.
> >> >> 
> >> >> 2. Change the series to make this property optional.  If it's not
> >> >> there then the code behaves like it always did.  This would address
> >> >> the "compatibility" problem but likely wouldn't actually help any real
> >> >> people, and it would be extra work.
> >> >> 
> >> >> 3. Redo the driver to deprecate all the old offsets / bits and just
> >> >> put the table in the driver, keyed off the compatible string and base
> >> >> address if the IO memory.
> >> >> 
> >> >> 
> >> >> I can't make this decision.  It's up to those folks who would be
> >> >> landing the patch and I'd be happy with any of them.  What I'm less
> >> >> happy with, however, is the indecision preventing forward progress.
> >> >> We should pick one of the above things and land it.  My own personal
> >> >> bias is #1: just land the series.  No real people will be hurt and
> >> >> it's just adding another property that matches the ones next to it.
> >> > 
> >> > I'd second that #1 . That whole type-c phy thingy never fully worked in
> >> > the past (some for the never used dp output), so personally I don't
> >> > have
> >> > issues with going that route.
> >> > 
> >> >>  From a long term perspective (AKA how I'd write the next driver like
> >> >> 
> >> >> this) I personally lean towards to "tables in the driver, not in the
> >> >> device tree" but quite honestly I'm happy to take whatever direction
> >> >> the maintainers give.
> >> > 
> >> > It looks like we're in agreement here :-) . GRF stuff should not leak
> >> > into
> >> > the devicetree, as it causes endless headaches later. But I guess we'll
> >> > need to live with the ones that happened so far.
> >> 
> >> So, the first step is: move all the private property of tcphy to
> >> drivers/phy/rockchip/phy-rockchip-typec.c.
> >> Second step: new a member: uphy-dp-sel.
> >> In my mind, we should have discussed these properties before, and then I
> >> moved them all into DTS.
> > 
> > Actually, I was agreeing with Doug, that we probably don't need to rework
> > the type-c phy driver. As most properties for it are in the devicetree
> > right now we'll need to support them for backwards-compatiblity anyway.
> > 
> > And yes, there probably was discussion over dts vs. driver-table when the
> > type-c driver was introduced, but I either missed it or wasn't firm enough
> > back then ;-) .
> > 
> > Hence the "we'll need to live with it" for the type-c phy, but should not
> > do similar things in future drivers.
> 
> So I guess now we're just waiting for some agreement from Kishon that
> he's willing to land the PHY change?  Heiko: presumably you could
> apply the DP change to drm-misc?  ...or is there some other process
> needed there?

I was lagging behind a bit with the drm-misc account request but have
done so now. So once I got the hang of how drm-misc works and Kishon
has picked the phy-part I can most likely push the drm part (or Sandy,
depending on who is faster).

As for process, I don't think there is special care necessary. When
you get the intermediate case of phy-change but no drm-change
everything will just revert to how it works now anyway.

Heiko
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