Re: [PATCH 8/8] drm/bridge: it66121: Allow link this driver as a lib

[Sui Jingfeng]

Hi,


On 2023/11/16 17:30, Dmitry Baryshkov wrote:
> On Thu, 16 Nov 2023 at 11:14, Sui Jingfeng <sui.jingfeng@xxxxxxxxx> wrote:
> > Hi,
> >
> > Thanks a lot for reviewing!
> >
> >
> > On 2023/11/15 00:30, Dmitry Baryshkov wrote:
> > > On Tue, 14 Nov 2023 at 17:09, Sui Jingfeng <sui.jingfeng@xxxxxxxxx> wrote:
> > > > From: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
> > > >
> > > > The it66121_create_bridge() and it66121_destroy_bridge() are added to
> > > > export the core functionalities. Create a connector manually by using
> > > > bridge connector helpers when link as a lib.
> > > >
> > > > Signed-off-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
> > > > ---
> > > >    drivers/gpu/drm/bridge/ite-it66121.c | 134 +++++++++++++++++++--------
> > > >    include/drm/bridge/ite-it66121.h     |  17 ++++
> > > >    2 files changed, 113 insertions(+), 38 deletions(-)
> > > >    create mode 100644 include/drm/bridge/ite-it66121.h
> > > >
> > > > diff --git a/drivers/gpu/drm/bridge/ite-it66121.c b/drivers/gpu/drm/bridge/ite-it66121.c
> > > > index 8971414a2a60..f5968b679c5d 100644
> > > > --- a/drivers/gpu/drm/bridge/ite-it66121.c
> > > > +++ b/drivers/gpu/drm/bridge/ite-it66121.c
> > > > @@ -22,6 +22,7 @@
> > > >
> > > >    #include <drm/drm_atomic_helper.h>
> > > >    #include <drm/drm_bridge.h>
> > > > +#include <drm/drm_bridge_connector.h>
> > > >    #include <drm/drm_edid.h>
> > > >    #include <drm/drm_modes.h>
> > > >    #include <drm/drm_print.h>
> > > > @@ -703,14 +704,32 @@ static int it66121_bridge_attach(struct drm_bridge *bridge,
> > > >                                    enum drm_bridge_attach_flags flags)
> > > >    {
> > > >           struct it66121_ctx *ctx = bridge_to_it66121(bridge);
> > > > +       struct drm_bridge *next_bridge = ctx->next_bridge;
> > > > +       struct drm_encoder *encoder = bridge->encoder;
> > > >           int ret;
> > > >
> > > > -       if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR))
> > > > -               return -EINVAL;
> > > > +       if (next_bridge) {
> > > > +               if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)) {
> > > > +                       WARN_ON(1);
> > > Why? At least use WARN() instead
> > Originally I want to
> >
> >
> >
> >
> > > > +                       flags |= DRM_BRIDGE_ATTACH_NO_CONNECTOR;
> > > > +               }
> > > > +               ret = drm_bridge_attach(encoder, next_bridge, bridge, flags);
> > > > +               if (ret)
> > > > +                       return ret;
> > > > +       } else {
> > > > +               struct drm_connector *connector;
> > > >
> > > > -       ret = drm_bridge_attach(bridge->encoder, ctx->next_bridge, bridge, flags);
> > > > -       if (ret)
> > > > -               return ret;
> > > > +               if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
> > > > +                       WARN_ON(1);
> > > No. It is perfectly fine to create attach a bridge with no next_bridge
> > > and with the DRM_BRIDGE_ATTACH_NO_CONNECTOR flag.
> > The document say when DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is set
> > the bridge shall not create a drm_connector. So I think if a display
> > bridge driver don't have a next bridge attached (Currently, this is
> > told by the DT), it says that this is a non-DT environment. On such
> > a case, this display bridge driver(it66121.ko) should behavior like
> > a *agent*. Because the upstream port of it66121 is the DVO port of
> > the display controller, the downstream port of it66121 is the HDMI
> > connector. it66121 is on the middle. So I think the it66121.ko should
> > handle all of troubles on behalf of the display controller drivers.
> No. Don't make decisions for the other drivers. They might have different needs.

[...]


> > Therefore (when in non-DT use case), the display controller drivers
> > side should not set DRM_BRIDGE_ATTACH_NO_CONNECTOR flag anymore.
> > Which is to hint that the it66121 should totally in charge of those
> > tasks (either by using bridge connector helper or create a connector
> > manually). I don't understand on such a case, why bother display
> > controller drivers anymore.
> This is the reason why we had introduced this flag. It allows the
> driver to customise the connector. It even allows the driver to
> implement a connector on its own, completely ignoring the
> drm_bridge_connector.


I know what you said is right in the sense of the universe cases,
but I think the most frequent(majority) use case is that there is
only one display bridge on the middle. Therefore, I don't want to
movethe connector things into device driver if there is only one display 
bridge(say it66121) in the middle. After all, there is no *direct 
physical connection* from the perspective of the hardware. I means that 
there is no hardware wires connectthe HDMI connector and the DVO port. So display controller drivers 
should not interact with anything related with the connector on a 
perfect abstract on the software side. Especially for such a simple use 
case. It probably make senses to make a  decision for themost frequently use case, please also note
that this patch didn't introduce any-restriction for the more advance
uses cases(multiple bridges in the middle).


> > > > +
> > > > +               connector = drm_bridge_connector_init(bridge->dev, encoder);
> > > > +               if (IS_ERR(connector))
> > > > +                       return PTR_ERR(connector);
> > > > +
> > > > +               drm_connector_attach_encoder(connector, encoder);
> > > This goes into your device driver.
> > >
> > > > +
> > > > +               ctx->connector = connector;
> > > > +       }
> > > >
> > > >           if (ctx->info->id == ID_IT66121) {
> > > >                   ret = regmap_write_bits(ctx->regmap, IT66121_CLK_BANK_REG,
> > > > @@ -1632,16 +1651,13 @@ static const char * const it66121_supplies[] = {
> > > >           "vcn33", "vcn18", "vrf12"
> > > >    };