linux-kernel - RE: [PATCH v4 5/5] drm: bridge: add support for Cadence MHDP DPI/DP bridge

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Date:   Mon, 24 Sep 2018 12:47:39 +0000
From:   Damian Kos <dkos@...ence.com>
To:     Heiko Stuebner <heiko@...ech.de>,
        Artur Jedrysek <jartur@...ence.com>,
        "jbergsagel@...com" <jbergsagel@...com>
CC:     David Airlie <airlied@...ux.ie>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Sean Paul <sean@...rly.run>, Sandy Huang <hjc@...k-chips.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-rockchip@...ts.infradead.org" 
        <linux-rockchip@...ts.infradead.org>,
        Piotr Sroka <piotrs@...ence.com>,
        Quentin Schulz <quentin.schulz@...e-electrons.com>
Subject: RE: [PATCH v4 5/5] drm: bridge: add support for Cadence MHDP DPI/DP
 bridge

Heiko,

> Hi Damian,
> 
> Am Montag, 24. September 2018, 13:40:03 CEST schrieb Damian Kos:
> > > Am Donnerstag, 20. September 2018, 16:54:40 CEST schrieb Damian Kos:
> > > > From: Quentin Schulz <quentin.schulz@...e-electrons.com>
> > > > 
> > > > This adds basic support for Cadence MHDP DPI to DP bridge.
> > > > 
> > > > Basically, it takes a DPI stream as input and output it encoded in 
> > > > DP format. It's missing proper HPD, HDCP and currently supports 
> > > > only SST mode.
> > > > 
> > > > Changes made in the low level driver (cdn-dp-reg.*):
> > > > - moved it to from drivers/gpu/drm/rockchip to
> > > >   drivers/gpu/drm/bridge/cdns-mhdp-common.*
> > > > - functions for sending/receiving commands are now public
> > > > - added functions for reading registers and link training
> > > >   adjustment
> > > > 
> > > > Changes made in RK's driver (cdn-dp-core.*):
> > > > - Moved audio_info and audio_pdev fields from cdn_dp_device to
> > > >   cdns_mhdp_device structure.
> > > > 
> > > > Signed-off-by: Quentin Schulz <quentin.schulz@...e-electrons.com>
> > > > Signed-off-by: Damian Kos <dkos@...ence.com>
> > > 
> > > [...]
> > > 
> > > > diff --git a/drivers/gpu/drm/rockchip/Kconfig
> > > > b/drivers/gpu/drm/rockchip/Kconfig
> > > > index 0ccc76217ee4..129b0529f3e1 100644
> > > > --- a/drivers/gpu/drm/rockchip/Kconfig
> > > > +++ b/drivers/gpu/drm/rockchip/Kconfig
> > > > @@ -27,7 +27,9 @@ config ROCKCHIP_ANALOGIX_DP
> > > >  
> > > >  config ROCKCHIP_CDN_DP
> > > >          bool "Rockchip cdn DP"
> > > > -	depends on EXTCON=y || (EXTCON=m && DRM_ROCKCHIP=m)
> > > > +	depends on DRM_ROCKCHIP=m
> > > 
> > > Sorry, I wasn't fast enough in my reply to you mail to catch that before your v4, but I don't think this is necessary.
> > > Instead I do guess, the select below should do the right thing by making EXTCON=y if DRM_ROCKCHIP=y.
> > > 
> > > Somewhat clumsily verified by making EXTCON=m in my defconfig and seeing get changed to y upon build, which I guess comes from a different "select" in the config.
> > > 
> > 
> > I've changed it to:
> > 
> > config ROCKCHIP_CDN_DP
> >         bool "Rockchip cdn DP"
> >         depends on DRM_ROCKCHIP
> >         select EXTCON if DRM_ROCKCHIP=y
> >         select DRM_CDNS_MHDP
> >         help...
> > 
> > and it seems that there are no issues. At least for me.
> > 
> > Please let me know if that's OK.
> 
> nope, just do "select EXTCON" . It works nicely and the above would not select EXTCON at all if the the rockchip-drm driver gets built into the kernel.

That's weird. I'm pretty sure that I've tried that and got circular dependency error, but now it's working fine. Anyway:

config ROCKCHIP_CDN_DP
        bool "Rockchip cdn DP"
        depends on DRM_ROCKCHIP
        select EXTCON
        select DRM_CDNS_MHDP
        help...

> 
> To be sure I just did a little experiment and added:
> 
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig index 4ad85c046dcd..64e2b096afd8 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -154,4 +154,11 @@ source "drivers/gpu/drm/bridge/ite/Kconfig"
>  
>  source "drivers/gpu/drm/bridge/synopsys/Kconfig"
>  
> +config DRM_TMP1
> +       tristate "option to select"
> +
> +config DRM_TMP2
> +       tristate "option doing the selecting"
> +       select DRM_TMP1
> +
> 
> If I select DRM_TMP2=m as module I end up with CONFIG_DRM_TMP1=m CONFIG_DRM_TMP2=m in the defconfig and wit DRM_TMP2=y it changes to CONFIG_DRM_TMP1=y CONFIG_DRM_TMP2=y
> 
> so all is well with just doing "select EXTCON" above and will select the correct "m" or "y" stance as needed.
> 
> 
> Heiko

--
Damian