[PATCH 0/2] drm/tidss: Delay reset if we have a splash-screen

[PATCH 0/2] drm/tidss: Delay reset if we have a splash-screen

[Tomi Valkeinen]

These two patches are part of a bigger work to improve splash-screen
support (i.e. the bootloader sets up the initial display, and we try to
keep that on the screen until something else (Weston/X11) takes over).

 Tomi

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
---
Tomi Valkeinen (2):
      drm/tidss: Add some support for splash-screen
      drm/tidss: Remove early fb

 drivers/gpu/drm/tidss/tidss_dispc.c | 126 ++++++++++++++++++++++++++++++++----
 drivers/gpu/drm/tidss/tidss_dispc.h |   5 ++
 drivers/gpu/drm/tidss/tidss_drv.c   |  38 ++++++++++-
 drivers/gpu/drm/tidss/tidss_drv.h   |   2 +
 4 files changed, 156 insertions(+), 15 deletions(-)
---
base-commit: aec8a40228acb385d60feec59b54573d307e60f3
change-id: 20250416-tidss-splash-3d8f328b7160

Best regards,
-- 
Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>

[PATCH 1/2] drm/tidss: Add some support for splash-screen

[Tomi Valkeinen]

Currently when the driver's probe is called, we do a full DSS reset. If
the bootloader has set up a splash-screen, the reset will disable the
video output, and after that it may still take time until the display is
usable (all the kernel modules have been loaded) and even more time
until the userspace is able to use the display.

In a perfect case tidss would take over the fb memory set up by the
bootloader, and use that memory for tidss's fbdev, thus retaining the
splash-screen. However, we're not there yet.

As a partial solution, this patch changes the driver so that the driver
will not reset (or change) the DSS registers until tidss_runtime_get()
is called when the display is being set up (because of fbdev modesetting
or modesetting from the userspace).

This is achieved in two parts:

1. Probe

At probe time, in dispc_check_hw_state(), we check if the DSS is idle
(videoports disabled). If yes, continue as before. If not, we know that
there's a splash-screen, and we set the 'tidss->boot_enabled_vp_mask'
field to reflect the enabled VP ports.

We then enable the corresponding VP clocks (to ensure they stay on), set
the IRQENABLE to 0 to make sure we won't get any interrupts, and then
exit leaving the fclk and VP clocks enabled, and the runtime PM status
active.

2. Runtime get

When the tidss_runtime_get() is called the first time, as indicated by
the 'boot_enabled_vp_mask', we know that we have the splash-screen
showing on the screen, and that the pm_runtime_resume_and_get() call in
tidss_runtime_get() did not cause a runtime_resume callback to get
called.

We call dispc_splash_fini() which essentially returns the DSS into the
state where it would be in a non-splash-screen case: dispc_splash_fini()
will do a DSS reset, manually call the runtime_resume callback, and then
call clk_disable_unprepare() and pm_runtime_put_noidle() to counter the
actions at probe time.

Finally 'boot_enabled_vp_mask' is set to zero to mark that we're no
longer in the "splash-screen mode".

===

A few notes:

If fbdev emulation is enabled in the DRM, tidss will set up an fbdev.
This will cause a modeset, and the blank framebuffer from tidss's fbdev
will be shown instead of the splash-screen.

I see two improvements to this: either we should memcpy the pixel data
from the bootloader's splash-screen to the new fbdev buffer, or the
fbdev could use the splash-screen directly as its buffer. I have done
some hacks for the former, but I'm not sure how to implement either of
these properly.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
---
 drivers/gpu/drm/tidss/tidss_dispc.c | 126 ++++++++++++++++++++++++++++++++----
 drivers/gpu/drm/tidss/tidss_dispc.h |   5 ++
 drivers/gpu/drm/tidss/tidss_drv.c   |  29 ++++++++-
 drivers/gpu/drm/tidss/tidss_drv.h   |   2 +
 4 files changed, 147 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c b/drivers/gpu/drm/tidss/tidss_dispc.c
index cacb5f3d8085..9504b775f6b1 100644
--- a/drivers/gpu/drm/tidss/tidss_dispc.c
+++ b/drivers/gpu/drm/tidss/tidss_dispc.c
@@ -2662,6 +2662,11 @@ void dispc_vp_setup(struct dispc_device *dispc, u32 hw_videoport,
 	dispc_vp_set_color_mgmt(dispc, hw_videoport, state, newmodeset);
 }
 
+static bool dispc_is_idle(struct dispc_device *dispc)
+{
+	return REG_GET(dispc, DSS_SYSSTATUS, 9, 9);
+}
+
 int dispc_runtime_suspend(struct dispc_device *dispc)
 {
 	dev_dbg(dispc->dev, "suspend\n");
@@ -2801,7 +2806,7 @@ static int dispc_softreset(struct dispc_device *dispc)
 	return 0;
 }
 
-static int dispc_init_hw(struct dispc_device *dispc)
+int dispc_init_hw(struct dispc_device *dispc)
 {
 	struct device *dev = dispc->dev;
 	int ret;
@@ -2818,15 +2823,69 @@ static int dispc_init_hw(struct dispc_device *dispc)
 		goto err_runtime_suspend;
 	}
 
-	ret = dispc_softreset(dispc);
-	if (ret)
-		goto err_clk_disable;
+	dispc->tidss->boot_enabled_vp_mask = 0;
 
-	clk_disable_unprepare(dispc->fclk);
-	ret = pm_runtime_set_suspended(dev);
-	if (ret) {
-		dev_err(dev, "Failed to set DSS PM to suspended\n");
-		return ret;
+	if (dispc_is_idle(dispc)) {
+		ret = dispc_softreset(dispc);
+		if (ret)
+			goto err_clk_disable;
+	} else {
+		for (u32 vp_idx = 0; vp_idx < dispc->feat->num_vps; vp_idx++) {
+			bool enabled = VP_REG_GET(dispc, vp_idx,
+						  DISPC_VP_CONTROL, 0, 0);
+
+			if (!enabled)
+				continue;
+
+			dispc->tidss->boot_enabled_vp_mask |= BIT(vp_idx);
+
+			/* Keep the VP clk enabled */
+			ret = clk_prepare_enable(dispc->vp_clk[vp_idx]);
+			if (ret) {
+				while (vp_idx--) {
+					if (!(dispc->tidss->boot_enabled_vp_mask &
+					      BIT(vp_idx)))
+						continue;
+
+					clk_disable_unprepare(dispc->vp_clk[vp_idx]);
+				}
+
+				goto err_clk_disable;
+			}
+		}
+
+		if (!dispc->tidss->boot_enabled_vp_mask) {
+			dev_warn(dev,
+				 "Bad HW state: DSS not idle but no VPs are enabled. Resetting.\n");
+			ret = dispc_softreset(dispc);
+			if (ret)
+				goto err_clk_disable;
+		} else {
+			/*
+			 * Do basic HW init here, which won't interrupt the
+			 * splash-screen.
+			 */
+
+			/* Ensure we won't get interrupts */
+			dispc_set_irqenable(dispc, 0);
+			dispc_read_and_clear_irqstatus(dispc);
+		}
+	}
+
+	if (dispc->tidss->boot_enabled_vp_mask) {
+		dev_dbg(dev,
+			"Bootloader splash-screen detected, leaving DSS active.\n");
+		pm_runtime_get_noresume(dev);
+	} else {
+		/*
+		 * No splash-screen. Disable the clock and set DSS back to suspended.
+		 */
+		clk_disable_unprepare(dispc->fclk);
+		ret = pm_runtime_set_suspended(dev);
+		if (ret) {
+			dev_err(dev, "Failed to set DSS PM to suspended\n");
+			return ret;
+		}
 	}
 
 	return 0;
@@ -2844,6 +2903,28 @@ static int dispc_init_hw(struct dispc_device *dispc)
 	return ret;
 }
 
+void dispc_init_hw_cleanup(struct dispc_device *dispc)
+{
+	if (!dispc->tidss->boot_enabled_vp_mask)
+		return;
+
+	/*
+	 * Call clk_disable_unprepare() to counter the clk_prepare_enable() we
+	 * did in the dispc_init_hw().
+	 */
+	clk_disable_unprepare(dispc->fclk);
+
+	for (u32 vp_idx = 0; vp_idx < dispc->feat->num_vps; vp_idx++) {
+		if (dispc->tidss->boot_enabled_vp_mask & BIT(vp_idx))
+			clk_disable_unprepare(dispc->vp_clk[vp_idx]);
+	}
+
+	/* counter the pm_runtime_get_noresume() */
+	pm_runtime_put_noidle(dispc->dev);
+
+	dispc->tidss->boot_enabled_vp_mask = 0;
+}
+
 int dispc_init(struct tidss_device *tidss)
 {
 	struct device *dev = tidss->dev;
@@ -2953,11 +3034,30 @@ int dispc_init(struct tidss_device *tidss)
 	of_property_read_u32(dispc->dev->of_node, "max-memory-bandwidth",
 			     &dispc->memory_bandwidth_limit);
 
-	r = dispc_init_hw(dispc);
-	if (r)
-		return r;
-
 	tidss->dispc = dispc;
 
 	return 0;
 }
+
+void dispc_splash_fini(struct dispc_device *dispc)
+{
+	if (WARN_ON(!dispc->tidss->boot_enabled_vp_mask))
+		return;
+
+	/*
+	 * Do a reset now, to clean up the bootloader setup, as we're about to
+	 * do a modeset.
+	 */
+	dispc_softreset(dispc);
+
+	/*
+	 * Call resume manually. This will clk_prepare_enable() the fclk, and do
+	 * the common basic HW configuration.
+	 */
+	dispc_runtime_resume(dispc);
+
+	/*
+	 * Revert the enables and gets we did in dispc_init_hw() at probe time.
+	 */
+	dispc_init_hw_cleanup(dispc);
+}
diff --git a/drivers/gpu/drm/tidss/tidss_dispc.h b/drivers/gpu/drm/tidss/tidss_dispc.h
index 086327d51a90..b407cbe65c9f 100644
--- a/drivers/gpu/drm/tidss/tidss_dispc.h
+++ b/drivers/gpu/drm/tidss/tidss_dispc.h
@@ -137,4 +137,9 @@ const u32 *dispc_plane_formats(struct dispc_device *dispc, unsigned int *len);
 int dispc_init(struct tidss_device *tidss);
 void dispc_remove(struct tidss_device *tidss);
 
+int dispc_init_hw(struct dispc_device *dispc);
+void dispc_init_hw_cleanup(struct dispc_device *dispc);
+
+void dispc_splash_fini(struct dispc_device *dispc);
+
 #endif
diff --git a/drivers/gpu/drm/tidss/tidss_drv.c b/drivers/gpu/drm/tidss/tidss_drv.c
index d4652e8cc28c..21f2358790b4 100644
--- a/drivers/gpu/drm/tidss/tidss_drv.c
+++ b/drivers/gpu/drm/tidss/tidss_drv.c
@@ -34,8 +34,22 @@ int tidss_runtime_get(struct tidss_device *tidss)
 	dev_dbg(tidss->dev, "%s\n", __func__);
 
 	r = pm_runtime_resume_and_get(tidss->dev);
-	WARN_ON(r < 0);
-	return r;
+	if (WARN_ON(r < 0))
+		return r;
+
+	if (tidss->boot_enabled_vp_mask) {
+		/*
+		 * If 'boot_enabled_vp_mask' is set, it means that the DSS is
+		 * enabled and bootloader splash-screen is still on the screen,
+		 * using bootloader's DSS HW config.
+		 *
+		 * This is the first time the driver is about to use the HW, and
+		 * we need to do some cleanup and initial setup.
+		 */
+		dispc_splash_fini(tidss->dispc);
+	}
+
+	return 0;
 }
 
 void tidss_runtime_put(struct tidss_device *tidss)
@@ -147,6 +161,12 @@ static int tidss_probe(struct platform_device *pdev)
 		return ret;
 	}
 
+	ret = dispc_init_hw(tidss->dispc);
+	if (ret) {
+		dev_err(dev, "failed to initialize dispc HW: %d\n", ret);
+		return ret;
+	}
+
 	pm_runtime_enable(dev);
 
 	pm_runtime_set_autosuspend_delay(dev, 1000);
@@ -197,12 +217,15 @@ static int tidss_probe(struct platform_device *pdev)
 	tidss_irq_uninstall(ddev);
 
 err_runtime_suspend:
+
 #ifndef CONFIG_PM
 	dispc_runtime_suspend(tidss->dispc);
 #endif
 	pm_runtime_dont_use_autosuspend(dev);
 	pm_runtime_disable(dev);
 
+	dispc_init_hw_cleanup(tidss->dispc);
+
 	return ret;
 }
 
@@ -227,6 +250,8 @@ static void tidss_remove(struct platform_device *pdev)
 	pm_runtime_dont_use_autosuspend(dev);
 	pm_runtime_disable(dev);
 
+	dispc_init_hw_cleanup(tidss->dispc);
+
 	/* devm allocated dispc goes away with the dev so mark it NULL */
 	dispc_remove(tidss);
 
diff --git a/drivers/gpu/drm/tidss/tidss_drv.h b/drivers/gpu/drm/tidss/tidss_drv.h
index 7f4f4282bc04..814727716d4d 100644
--- a/drivers/gpu/drm/tidss/tidss_drv.h
+++ b/drivers/gpu/drm/tidss/tidss_drv.h
@@ -32,6 +32,8 @@ struct tidss_device {
 	/* protects the irq masks field and irqenable/irqstatus registers */
 	spinlock_t irq_lock;
 	dispc_irq_t irq_mask;	/* enabled irqs */
+
+	u32 boot_enabled_vp_mask;
 };
 
 #define to_tidss(__dev) container_of(__dev, struct tidss_device, ddev)

-- 
2.43.0

[PATCH 2/2] drm/tidss: Remove early fb

[Tomi Valkeinen]

Add a call to drm_aperture_remove_framebuffers() to drop the possible
early fb (simplefb).

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
---
 drivers/gpu/drm/tidss/tidss_drv.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/tidss/tidss_drv.c b/drivers/gpu/drm/tidss/tidss_drv.c
index 21f2358790b4..17df0583710c 100644
--- a/drivers/gpu/drm/tidss/tidss_drv.c
+++ b/drivers/gpu/drm/tidss/tidss_drv.c
@@ -8,6 +8,7 @@
 #include <linux/of.h>
 #include <linux/module.h>
 #include <linux/pm_runtime.h>
+#include <linux/aperture.h>
 
 #include <drm/clients/drm_client_setup.h>
 #include <drm/drm_atomic.h>
@@ -207,12 +208,20 @@ static int tidss_probe(struct platform_device *pdev)
 		goto err_irq_uninstall;
 	}
 
+	/* Remove possible early fb before setting up the fbdev */
+	ret = aperture_remove_all_conflicting_devices(tidss_driver.name);
+	if (ret)
+		goto err_drm_dev_unreg;
+
 	drm_client_setup(ddev, NULL);
 
 	dev_dbg(dev, "%s done\n", __func__);
 
 	return 0;
 
+err_drm_dev_unreg:
+	drm_dev_unregister(ddev);
+
 err_irq_uninstall:
 	tidss_irq_uninstall(ddev);
 

-- 
2.43.0

Re: [PATCH 1/2] drm/tidss: Add some support for splash-screen

[Maxime Ripard]

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Hi Tomi,

On Wed, Apr 16, 2025 at 02:06:29PM +0300, Tomi Valkeinen wrote:
> Currently when the driver's probe is called, we do a full DSS reset. If
> the bootloader has set up a splash-screen, the reset will disable the
> video output, and after that it may still take time until the display is
> usable (all the kernel modules have been loaded) and even more time
> until the userspace is able to use the display.
> 
> In a perfect case tidss would take over the fb memory set up by the
> bootloader, and use that memory for tidss's fbdev, thus retaining the
> splash-screen. However, we're not there yet.
> 
> As a partial solution, this patch changes the driver so that the driver
> will not reset (or change) the DSS registers until tidss_runtime_get()
> is called when the display is being set up (because of fbdev modesetting
> or modesetting from the userspace).
> 
> This is achieved in two parts:
> 
> 1. Probe
> 
> At probe time, in dispc_check_hw_state(), we check if the DSS is idle
> (videoports disabled). If yes, continue as before. If not, we know that
> there's a splash-screen, and we set the 'tidss->boot_enabled_vp_mask'
> field to reflect the enabled VP ports.
> 
> We then enable the corresponding VP clocks (to ensure they stay on), set
> the IRQENABLE to 0 to make sure we won't get any interrupts, and then
> exit leaving the fclk and VP clocks enabled, and the runtime PM status
> active.
> 
> 2. Runtime get
> 
> When the tidss_runtime_get() is called the first time, as indicated by
> the 'boot_enabled_vp_mask', we know that we have the splash-screen
> showing on the screen, and that the pm_runtime_resume_and_get() call in
> tidss_runtime_get() did not cause a runtime_resume callback to get
> called.
> 
> We call dispc_splash_fini() which essentially returns the DSS into the
> state where it would be in a non-splash-screen case: dispc_splash_fini()
> will do a DSS reset, manually call the runtime_resume callback, and then
> call clk_disable_unprepare() and pm_runtime_put_noidle() to counter the
> actions at probe time.
> 
> Finally 'boot_enabled_vp_mask' is set to zero to mark that we're no
> longer in the "splash-screen mode".
> 
> ===
> 
> A few notes:
> 
> If fbdev emulation is enabled in the DRM, tidss will set up an fbdev.
> This will cause a modeset, and the blank framebuffer from tidss's fbdev
> will be shown instead of the splash-screen.
> 
> I see two improvements to this: either we should memcpy the pixel data
> from the bootloader's splash-screen to the new fbdev buffer, or the
> fbdev could use the splash-screen directly as its buffer. I have done
> some hacks for the former, but I'm not sure how to implement either of
> these properly.

So, DRM kind of has support for it, but not really.

What you're trying to do is essentially what i915 fastboot is about:
booting flicker-free, and speeding up the probe process.

i915 does so using two things:

  * IIRC, the UEFI exposes its splashscreen through ACPI, and this in
    turn is exposed through sysfs. Plymouth then picks it up, and does
    its own thing with it. I think it would be fairly easy to do
    something similar for simple-drm: the memory is typically reserved,
    so it will stick around, and you just need to expose the memory
    buffer as a sysfs file. If we want to make it simpler, I guess we
    could expose it as BMP, and that would possibly require a format
    conversion. But yeah, it shouldn't be too hard.

  * Then, the i915 driver has a custom reset hook. reset() is about
    building the initial state, and most drivers actually go from a
    pristine state. However, nothing prevents a driver from building a
    custom initial state by building it from the register. Then, you'll
    only get a flicker if the compositor initial modeset actually
    requires a modeset. Otherwise, you can just do a page flip.

We discussed it with Sima in the past, and here's a more detailed
description of what it would entail:

https://lore.kernel.org/dri-devel/CAKMK7uHtqHy_oz4W7F+hmp9iqp7W5Ra8CxPvJ=9BwmvfU-O0gg@mail.gmail.com/

Maxime

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Re: [PATCH 2/2] drm/tidss: Remove early fb

[Javier Martinez Canillas]

Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> writes:

Hello Tomi,

> Add a call to drm_aperture_remove_framebuffers() to drop the possible
> early fb (simplefb).
>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> ---

This patch can be picked and is independant of how the other one.

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat

Re: [PATCH 2/2] drm/tidss: Remove early fb

[Tomi Valkeinen]

Hi,

On 10/07/2025 14:59, Javier Martinez Canillas wrote:
> Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> writes:
> 
> Hello Tomi,
> 
>> Add a call to drm_aperture_remove_framebuffers() to drop the possible
>> early fb (simplefb).
>>
>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
>> ---
> 
> This patch can be picked and is independant of how the other one.
> 
> Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>

Indeed, I'll apply this one. Thanks!

 Tomi