linux-kernel - [PATCH 4/9] drm/msm: Avoid manually populating our children if "simple-bus" is there

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Message-Id: <20200710160131.4.I358ea82de218ea5f4406572ade23f5e121297555@changeid>
Date:   Fri, 10 Jul 2020 16:02:19 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     Rob Herring <robh+dt@...nel.org>, Rob Clark <robdclark@...il.com>,
        Sean Paul <sean@...rly.run>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org
Subject: [PATCH 4/9] drm/msm: Avoid manually populating our children if "simple-bus" is there

If our compatible string has "simple-bus" at the end of it then the
system will handle probing our children for us.  Doing this has a few
advantages:

1. If we defer we don't have to keep probing / removing our children
   which should speed up boot.  The system just probes them once.

2. It fixes a problem where we could get into a big loop where we'd
   have:
   - msm_pdev_probe() is called.
   - msm_pdev_probe() registers drivers.  Registering drivers kicks
     off processing of probe deferrals.
   - component_master_add_with_match() could return -EPROBE_DEFER.
     making msm_pdev_probe() return -EPROBE_DEFER.
   - When msm_pdev_probe() returned the processing of probe deferrals
     happens.
   - Loop back to the start.

Signed-off-by: Douglas Anderson <dianders@...omium.org>
---

 drivers/gpu/drm/msm/msm_drv.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
index 78b09fde9e29..f7c6ef147095 100644
--- a/drivers/gpu/drm/msm/msm_drv.c
+++ b/drivers/gpu/drm/msm/msm_drv.c
@@ -1208,10 +1208,18 @@ static int add_display_components(struct device *dev,
 	if (of_device_is_compatible(dev->of_node, "qcom,mdss") ||
 	    of_device_is_compatible(dev->of_node, "qcom,sdm845-mdss") ||
 	    of_device_is_compatible(dev->of_node, "qcom,sc7180-mdss")) {
-		ret = devm_of_platform_populate(dev);
-		if (ret) {
-			DRM_DEV_ERROR(dev, "failed to populate children devices\n");
-			return ret;
+		/*
+		 * Old device tree files didn't include "simple-bus"
+		 * in their compatible string so we had to manually pouplate
+		 * our children.  When existing device trees are fixed this
+		 * can be removed.
+		 */
+		if (!of_device_is_compatible(dev->of_node, "simple-bus")) {
+			ret = devm_of_platform_populate(dev);
+			if (ret) {
+				DRM_DEV_ERROR(dev, "failed to populate children devices\n");
+				return ret;
+			}
 		}
 
 		mdp_dev = device_find_child(dev, NULL, compare_name_mdp);
-- 
2.27.0.383.g050319c2ae-goog