linux-kernel - Re: [PATCH v3 4/5] drm: convert drivers to use drm_of_find_panel_or

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Date:   Tue, 9 May 2017 17:28:21 +0300
From:   Leonard Crestez <leonard.crestez@....com>
To:     Rob Herring <robh@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>
CC:     <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        "Cristina Ciocan" <cristina-mihaela.ciocan@....com>,
        Octavian Purdila <octavian.purdila@....com>
Subject: Re: [PATCH v3 4/5] drm: convert drivers to use
 drm_of_find_panel_or_bridge

On Wed, Mar 22, 2017 at 5:01 PM, Philipp Zabel <p.zabel@...gutronix.de> wrote:
> On Wed, 2017-03-22 at 08:26 -0500, Rob Herring wrote:
> > 
> > Similar to the previous commit, convert drivers open coding OF graph
> > parsing to use drm_of_find_panel_or_bridge instead.
> > 
> > This changes some error messages to debug messages (in the graph core).
> > Graph connections are often "no connects" depending on the particular
> > board, so we want to avoid spurious messages. Plus the kernel is not a
> > DT validator.
> > 
> > Signed-off-by: Rob Herring <robh@...nel.org>
> > Reviewed-by: Archit Taneja <architt@...eaurora.org>
> Tested-by: Philipp Zabel <p.zabel@...gutronix.de>
> (imx-ldb on i.MX6)

It seems that this breaks on (at least) imx6qdl-sabreauto. The relevant
section of the boot log looks like this:

imx-drm display-subsystem: bound imx-ipuv3-crtc.2 (ops ipu_crtc_ops)
imx-drm display-subsystem: bound imx-ipuv3-crtc.3 (ops ipu_crtc_ops)
dwhdmi-imx 120000.hdmi: Detected HDMI TX controller v1.31a with HDCP
(DWC HDMI 3D TX PHY)
dwhdmi-imx 120000.hdmi: registered DesignWare HDMI I2C bus driver
imx-drm display-subsystem: bound 120000.hdmi (ops dw_hdmi_imx_ops)
imx-drm display-subsystem: failed to bind 2000000.aips-bus:ldb (ops
imx_ldb_ops): -19
imx-drm display-subsystem: master bind failed: -19

It seems that imx6qdl-sabreauto does not have any panel defined in dts.
This used to be ignored when of_graph_get_endpoint_by_regs returned
NULL but now drm_of_find_panel_or_bridge returns -ENODEV and this
causes imx_ldb_bind to fail altogether. Defining a panel works
(including showing stuff on a LVDS panel). Ignoring -ENODEV also fixes
this:

--- drivers/gpu/drm/imx/imx-ldb.c
+++ drivers/gpu/drm/imx/imx-ldb.c
@@ -673,7 +673,7 @@ static int imx_ldb_bind(struct device *dev, struct device *master, void *data)
                ret = drm_of_find_panel_or_bridge(child,
                                                  imx_ldb->lvds_mux ? 4 : 2, 0,
                                                  &channel->panel, &channel->bridge);
-               if (ret)
+               if (ret != -ENODEV)
                        return ret;
 
                /* panel ddc only if there is no bridge */

I don't know much about drm and it's not clear if failing to find a
panel should be an error here or not and the hack above is likely the
wrong way to handle it anyway.

I was bisecting the fact that suspend now breaks on upstream. The fact
that a probe error later breaks suspend is possibly an unrelated issue,
right?

-- 
Regards,
Leonard