linux-kernel - [RFC PATCH 1/4] drm/etnaviv: Prevent IRQ triggering at probe time on i.MX8MM

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Date:   Thu, 30 Apr 2020 12:46:07 +0000
From:   Schrempf Frieder <frieder.schrempf@...tron.de>
To:     Adam Ford <aford173@...il.com>, Anson Huang <Anson.Huang@....com>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        Daniel Baluta <daniel.baluta@....com>,
        Fabio Estevam <festevam@...il.com>,
        Schrempf Frieder <frieder.schrempf@...tron.de>,
        Leonard Crestez <leonard.crestez@....com>,
        "Li Jun" <jun.li@....com>, Lucas Stach <l.stach@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        Peng Fan <peng.fan@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        "Sascha Hauer" <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        "S.j. Wang" <shengjiu.wang@....com>
CC:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "etnaviv@...ts.freedesktop.org" <etnaviv@...ts.freedesktop.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [RFC PATCH 1/4] drm/etnaviv: Prevent IRQ triggering at probe time on
 i.MX8MM

From: Frieder Schrempf <frieder.schrempf@...tron.de>

On i.MX8MM there is an interrupt getting triggered immediately after
requesting the IRQ, which leads to a stall as the handler accesses
the GPU registers whithout the clock being enabled.

Enabling the clocks briefly seems to clear the IRQ state, so we do
this before requesting the IRQ.

Signed-off-by: Frieder Schrempf <frieder.schrempf@...tron.de>
---
 drivers/gpu/drm/etnaviv/etnaviv_gpu.c | 29 ++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
index a31eeff2b297..23877c1f150a 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
@@ -1775,13 +1775,6 @@ static int etnaviv_gpu_platform_probe(struct platform_device *pdev)
 		return gpu->irq;
 	}
 
-	err = devm_request_irq(&pdev->dev, gpu->irq, irq_handler, 0,
-			       dev_name(gpu->dev), gpu);
-	if (err) {
-		dev_err(dev, "failed to request IRQ%u: %d\n", gpu->irq, err);
-		return err;
-	}
-
 	/* Get Clocks: */
 	gpu->clk_reg = devm_clk_get(&pdev->dev, "reg");
 	DBG("clk_reg: %p", gpu->clk_reg);
@@ -1805,6 +1798,28 @@ static int etnaviv_gpu_platform_probe(struct platform_device *pdev)
 		gpu->clk_shader = NULL;
 	gpu->base_rate_shader = clk_get_rate(gpu->clk_shader);
 
+	/*
+	 * On i.MX8MM there is an interrupt getting triggered immediately
+	 * after requesting the IRQ, which leads to a stall as the handler
+	 * accesses the GPU registers whithout the clock being enabled.
+	 * Enabling the clocks briefly seems to clear the IRQ state, so we do
+	 * this here before requesting the IRQ.
+	 */
+	err = etnaviv_gpu_clk_enable(gpu);
+	if (err)
+		return err;
+
+	err = etnaviv_gpu_clk_disable(gpu);
+	if (err)
+		return err;
+
+	err = devm_request_irq(&pdev->dev, gpu->irq, irq_handler, 0,
+			       dev_name(gpu->dev), gpu);
+	if (err) {
+		dev_err(dev, "failed to request IRQ%u: %d\n", gpu->irq, err);
+		return err;
+	}
+
 	/* TODO: figure out max mapped size */
 	dev_set_drvdata(dev, gpu);
 
-- 
2.17.1