Re: [PATCH] arm64: dts: qcom: sc8280xp-x13s: Use the correct DP PHY compatible

[Bjorn Andersson]

On Mon, Oct 16, 2023 at 12:10:18PM +0300, Dmitry Baryshkov wrote:
> On Mon, 16 Oct 2023 at 12:01, Johan Hovold <johan@xxxxxxxxxx> wrote:
> >
> > On Mon, Oct 16, 2023 at 11:51:33AM +0300, Dmitry Baryshkov wrote:
> > > On Fri, 29 Sept 2023 at 19:03, Konrad Dybcio <konrad.dybcio@xxxxxxxxxx> wrote:
> > > >
> > > > The DP PHY needs different settings when an eDP display is used.
> > > > Make sure these apply on the X13s.
> > >
> > > Could you please clarify, is it the same PHY type, just being
> > > repurposed for eDP or is it a different PHY type?
> >
> > Same PHY, just different settings AFAIK.
> >
> > > If the former is the case (and the same PHY can be used for both DP
> > > and eDP), it should carry the same compatible string and use software
> > > mechanisms (e.g. phy_set_mode_ext()) to be programmed for the correct
> > > operation mode.
> >
> > Possibly, but that's not how the current binding and implementation
> > works:
> >
> >         6993c079cd58 ("dt-bindings: phy: qcom-edp: Add SC8280XP PHY compatibles")
> >         2300d1cb24b3 ("phy: qcom: edp: Introduce support for DisplayPort")
> >         3b7267dec445 ("phy: qcom: edp: Add SC8280XP eDP and DP PHYs")
> >
> >         https://lore.kernel.org/lkml/20220810040745.3582985-1-bjorn.andersson@xxxxxxxxxx/
> >
> > And you'd still need to infer the mode from DT somehow.
> 
> If it is the same hardware block, it seems incorrect to have two
> different compat entries. For example, for PCIe RC vs PCIe EP we
> specify the PHY mode from the host controller driver.
> I'd say, we need to fix the bindings for both DP/eDP controller and
> the PHY.  See the `phy-mode` DT property for example.
> 

It is one hardware block, supporting both eDP and DP, so I like your
suggestion of having a single compatible instead and using some other
means of defining the configuration. I just wasn't able to find a
better way to do so back when I wrote the binding/driver...

Regards,
Bjorn