linux-kernel - Re: [PATCH v5 5/6] drm: lcdif: Add multiple encoders and first bridges support

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Message-ID: <CAOcKUNXzyjK+xUp2an69ExsLhWDi8gZt0suZM88jrCc2M_BqNg@mail.gmail.com>
Date:   Wed, 10 May 2023 16:44:48 +0800
From:   Ying Liu <gnuiyl@...il.com>
To:     Marek Vasut <marex@...x.de>
Cc:     Liu Ying <victor.liu@....com>, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, conor+dt@...nel.org,
        alexander.stein@...tq-group.com, shawnguo@...nel.org,
        s.hauer@...gutronix.de, krzysztof.kozlowski@...aro.org,
        robh+dt@...nel.org, linux-imx@....com,
        krzysztof.kozlowski+dt@...aro.org, kernel@...gutronix.de,
        LW@...o-electronics.de
Subject: Re: [PATCH v5 5/6] drm: lcdif: Add multiple encoders and first
 bridges support

On Tue, May 9, 2023 at 10:14 AM Marek Vasut <marex@...x.de> wrote:
>
> On 5/8/23 07:57, Liu Ying wrote:
> > The single LCDIF embedded in i.MX93 SoC may drive multiple displays
> > simultaneously.  Look at LCDIF output port's remote port parents to
> > find all enabled first bridges.  Add an encoder for each found bridge
> > and attach the bridge to the encoder.  This is a preparation for
> > adding i.MX93 LCDIF support.
> >
> > Tested-by: Alexander Stein <alexander.stein@...tq-group.com>
> > Acked-by: Alexander Stein <alexander.stein@...tq-group.com>
> > Signed-off-by: Liu Ying <victor.liu@....com>
> > ---
> > v4->v5:
> > * Rebase upon v6.4-rc1 and resolve a trivial conflict.
> > * Add Alexander's A-b and T-b tags.
> >
> > v3->v4:
> > * Improve warning message when ignoring invalid LCDIF OF endpoint ids.
> >    (Alexander)
> >
> > v2->v3:
> > * No change.
> >
> > v1->v2:
> > * Split from patch 2/2 in v1. (Marek, Alexander)
> > * Drop '!remote ||' from lcdif_attach_bridge(). (Lothar)
> > * Drop unneeded 'bridges' member from lcdif_drm_private structure.
> >
> >   drivers/gpu/drm/mxsfb/lcdif_drv.c | 68 +++++++++++++++++++++++++++----
> >   drivers/gpu/drm/mxsfb/lcdif_drv.h |  4 +-
> >   drivers/gpu/drm/mxsfb/lcdif_kms.c | 21 ++--------
> >   3 files changed, 66 insertions(+), 27 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/mxsfb/lcdif_drv.c b/drivers/gpu/drm/mxsfb/lcdif_drv.c
> > index e816f87828fb..cf27b63b1899 100644
> > --- a/drivers/gpu/drm/mxsfb/lcdif_drv.c
> > +++ b/drivers/gpu/drm/mxsfb/lcdif_drv.c
> > @@ -9,13 +9,16 @@
> >   #include <linux/dma-mapping.h>
> >   #include <linux/io.h>
> >   #include <linux/module.h>
> > +#include <linux/of.h>
> >   #include <linux/of_device.h>
> > +#include <linux/of_graph.h>
> >   #include <linux/platform_device.h>
> >   #include <linux/pm_runtime.h>
> >
> >   #include <drm/drm_atomic_helper.h>
> >   #include <drm/drm_bridge.h>
> >   #include <drm/drm_drv.h>
> > +#include <drm/drm_encoder.h>
> >   #include <drm/drm_fbdev_dma.h>
> >   #include <drm/drm_gem_dma_helper.h>
> >   #include <drm/drm_gem_framebuffer_helper.h>
> > @@ -38,19 +41,68 @@ static const struct drm_mode_config_helper_funcs lcdif_mode_config_helpers = {
> >       .atomic_commit_tail = drm_atomic_helper_commit_tail_rpm,
> >   };
> >
> > +static const struct drm_encoder_funcs lcdif_encoder_funcs = {
> > +     .destroy = drm_encoder_cleanup,
> > +};
> > +
> >   static int lcdif_attach_bridge(struct lcdif_drm_private *lcdif)
> >   {
> > -     struct drm_device *drm = lcdif->drm;
> > +     struct device *dev = lcdif->drm->dev;
> > +     struct device_node *ep;
> >       struct drm_bridge *bridge;
> >       int ret;
> >
> > -     bridge = devm_drm_of_get_bridge(drm->dev, drm->dev->of_node, 0, 0);
> > -     if (IS_ERR(bridge))
> > -             return PTR_ERR(bridge);
> > -
> > -     ret = drm_bridge_attach(&lcdif->encoder, bridge, NULL, 0);
> > -     if (ret)
> > -             return dev_err_probe(drm->dev, ret, "Failed to attach bridge\n");
> > +     for_each_endpoint_of_node(dev->of_node, ep) {
> > +             struct device_node *remote;
> > +             struct of_endpoint of_ep;
> > +             struct drm_encoder *encoder;
> > +
> > +             remote = of_graph_get_remote_port_parent(ep);
> > +             if (!of_device_is_available(remote)) {
> > +                     of_node_put(remote);
> > +                     continue;
> > +             }
> > +             of_node_put(remote);
> > +
> > +             ret = of_graph_parse_endpoint(ep, &of_ep);
> > +             if (ret < 0) {
> > +                     dev_err(dev, "Failed to parse endpoint %pOF\n", ep);
> > +                     of_node_put(ep);
> > +                     return ret;
> > +             }
> > +
> > +             if (of_ep.id >= MAX_DISPLAYS) {
>
> Can we make the maximum number of displays, or really bridge, specific
> to IP instance instead (1 for mx8mp, 3 for mx93) ? If so, then I think
> we need to track a list of bridges in some linked list or some such
> dynamic structure, which would allow us to get rid of MAX_DISPLAYS macro.

I don't think we need to track bridges, since bridges can be found
through connector's encoder, like  lcdif_crtc_atomic_check() does
in patch 4/6.  Instead, MAX_DISPLAYS and the encoder member
in struct lcdif_drm_private can be dropped if we call devm_kzalloc()
to allocate encoders in this function.

>
> > +                     dev_warn(dev, "ingoring invalid endpoint id %u\n", of_ep.id);
>
> s@...oring@...oring@

Right.  But the endpoint id check is not mandatory and is better
to be dropped together with MAX_DISPLAYS.  I mean the driver
doesn't have to validate the endpoint id set in device tree.

Regards,
Liu Ying

>
> [...]