[PATCH v2 2/2] drm/msm/dpu: Issue MDSS reset during initialization

[Bjorn Andersson <bjorn.andersson@linaro.org>]

It's typical for the bootloader to bring up the display for showing a
boot splash or efi framebuffer. But in some cases the kernel driver ends
up only partially configuring (in particular) the DPU, which might
result in e.g. that two different data paths attempts to push data to
the interface - with resulting graphical artifacts.

Naturally the end goal would be to inherit the bootloader's
configuration and provide the user with a glitch free handover from the
boot configuration to a running DPU.

But as implementing seamless transition from the bootloader
configuration to the running OS will be a considerable effort, start by
simply resetting the entire MDSS to its power-on state, to avoid the
partial configuration.

Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
---

Changes since v2:
- Move the reset before the probing of the children, to avoid issues if child
  drivers touched hardware at probe time.
- Extend reset assert time as the previous 1us showed reliability issues on
  Lenovo Flex 5G.

 drivers/gpu/drm/msm/disp/dpu1/dpu_mdss.c | 32 ++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_mdss.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_mdss.c
index b10ca505f9ac..6f921910d0e0 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_mdss.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_mdss.c
@@ -3,10 +3,12 @@
  * Copyright (c) 2018, The Linux Foundation
  */
 
+#include <linux/delay.h>
 #include <linux/irq.h>
 #include <linux/irqchip.h>
 #include <linux/irqdesc.h>
 #include <linux/irqchip/chained_irq.h>
+#include <linux/reset.h>
 #include "dpu_kms.h"
 
 #define to_dpu_mdss(x) container_of(x, struct dpu_mdss, base)
@@ -197,6 +199,32 @@ static void dpu_mdss_destroy(struct msm_mdss *mdss)
 	dpu_mdss->mmio = NULL;
 }
 
+static int dpu_mdss_reset(struct device *dev)
+{
+	struct reset_control *reset;
+
+	reset = reset_control_get_optional_exclusive(dev, NULL);
+	if (!reset) {
+		/* Optional reset not specified */
+		return 0;
+	} else if (IS_ERR(reset)) {
+		DPU_ERROR("failed to acquire mdss reset, ret=%ld", PTR_ERR(reset));
+		return PTR_ERR(reset);
+	}
+
+	reset_control_assert(reset);
+	/*
+	 * Tests indicate that reset has to be held for some period of time,
+	 * make it one frame in a typical system
+	 */
+	msleep(20);
+	reset_control_deassert(reset);
+
+	reset_control_put(reset);
+
+	return 0;
+}
+
 static const struct msm_mdss_funcs mdss_funcs = {
 	.enable	= dpu_mdss_enable,
 	.disable = dpu_mdss_disable,
@@ -210,6 +238,10 @@ int dpu_mdss_init(struct platform_device *pdev)
 	int ret;
 	int irq;
 
+	ret = dpu_mdss_reset(&pdev->dev);
+	if (ret)
+		return ret;
+
 	dpu_mdss = devm_kzalloc(&pdev->dev, sizeof(*dpu_mdss), GFP_KERNEL);
 	if (!dpu_mdss)
 		return -ENOMEM;
-- 
2.35.1