linux-kernel - Re: [PATCH v4 1/4] drm: sun4i: dsi: Use drm_of_find_panel_or

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Message-ID: <CAMty3ZDOVeMeYTsuF8n4EQTG6eEbj6e33TuTPrFiMWG4RhRdSw@mail.gmail.com>
Date:   Wed, 24 Mar 2021 14:44:57 +0530
From:   Jagan Teki <jagan@...rulasolutions.com>
To:     Samuel Holland <samuel@...lland.org>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-amarula <linux-amarula@...rulasolutions.com>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH v4 1/4] drm: sun4i: dsi: Use drm_of_find_panel_or_bridge

On Wed, Mar 24, 2021 at 8:18 AM Samuel Holland <samuel@...lland.org> wrote:
>
> On 3/23/21 5:53 PM, Laurent Pinchart wrote:
> > Hi Jagan,
> >
> > Thank you for the patch.
> >
> > On Mon, Mar 22, 2021 at 07:31:49PM +0530, Jagan Teki wrote:
> >> Replace of_drm_find_panel with drm_of_find_panel_or_bridge
> >> for finding panel, this indeed help to find the bridge if
> >> bridge support added.
> >>
> >> Added NULL in bridge argument, same will replace with bridge
> >> parameter once bridge supported.
> >>
> >> Signed-off-by: Jagan Teki <jagan@...rulasolutions.com>
> >
> > Looks good, there should be no functional change.
>
> Actually this breaks all existing users of this driver, see below.
>
> > Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> >
> >> ---
> >> Changes for v4, v3:
> >> - none
> >>
> >>  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 11 ++++++++---
> >>  1 file changed, 8 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> >> index 4f5efcace68e..2e9e7b2d4145 100644
> >> --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> >> +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> >> @@ -21,6 +21,7 @@
> >>
> >>  #include <drm/drm_atomic_helper.h>
> >>  #include <drm/drm_mipi_dsi.h>
> >> +#include <drm/drm_of.h>
> >>  #include <drm/drm_panel.h>
> >>  #include <drm/drm_print.h>
> >>  #include <drm/drm_probe_helper.h>
> >> @@ -963,10 +964,14 @@ static int sun6i_dsi_attach(struct mipi_dsi_host *host,
> >>                          struct mipi_dsi_device *device)
> >>  {
> >>      struct sun6i_dsi *dsi = host_to_sun6i_dsi(host);
> >> -    struct drm_panel *panel = of_drm_find_panel(device->dev.of_node);
>
> This is using the OF node of the DSI device, which is a direct child of
> the DSI host's OF node. There is no OF graph involved.
>
> >> +    struct drm_panel *panel;
> >> +    int ret;
> >> +
> >> +    ret = drm_of_find_panel_or_bridge(dsi->dev->of_node, 0, 0,
> >> +                                      &panel, NULL);
>
> However, this function expects to find the panel using OF graph. This
> does not work with existing device trees (PinePhone, PineTab) which do
> not use OF graph to connect the panel. And it cannot work, because the
> DSI host's binding specifies a single port: the input port from the
> display engine.

Thanks for noticing this. I did understand your point and yes, I did
mention the updated pipeline in previous versions and forgot to add it
to this series.

Here is the updated pipeline to make it work:

https://patchwork.kernel.org/project/dri-devel/patch/20190524104252.20236-1-jagan@amarulasolutions.com/

Let me know your comments on this, so I will add a patch for the
above-affected DTS files.

Jagan.