drm/msm/dpu: Issue MDSS reset during initialization

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>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/482796/
Link: https://lore.kernel.org/r/20220421041550.643964-2-bjorn.andersson@linaro.orgSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/msm_mdss.c

@@ -4,11 +4,13 @@
  */
 
 #include <linux/clk.h>
+#include <linux/delay.h>
 #include <linux/irq.h>
 #include <linux/irqchip.h>
 #include <linux/irqdesc.h>
 #include <linux/irqchip/chained_irq.h>
 #include <linux/pm_runtime.h>
+#include <linux/reset.h>
 
 #include "msm_drv.h"
 #include "msm_kms.h"
@@ -193,6 +195,32 @@ static void msm_mdss_destroy(struct msm_mdss *msm_mdss)
 	irq_set_chained_handler_and_data(irq, NULL, NULL);
 }
 
+static int msm_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)) {
+		return dev_err_probe(dev, PTR_ERR(reset),
+				     "failed to acquire mdss reset\n");
+	}
+
+	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;
+}
+
 /*
  * MDP5 MDSS uses at most three specified clocks.
  */
@@ -229,6 +257,10 @@ static struct msm_mdss *msm_mdss_init(struct platform_device *pdev, bool is_mdp5
 	int ret;
 	int irq;
 
+	ret = msm_mdss_reset(&pdev->dev);
+	if (ret)
+		return ERR_PTR(ret);
+
 	msm_mdss = devm_kzalloc(&pdev->dev, sizeof(*msm_mdss), GFP_KERNEL);
 	if (!msm_mdss)
 		return ERR_PTR(-ENOMEM);