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 14:28:07 +0200
From:   Heiko Stuebner <heiko@...ech.de>
To:     Damian Kos <dkos@...ence.com>, 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

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.

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