AM625: AM62x LCD logo smooth transition between uboot and kernel

Hi,

The screen flash happens because of the following code: https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/commit/drivers/gpu/drm/tidss?h=ti-linux-6.1.y&id=c9b2d923befd8cee0b9d6cbd96128ec0bf44c881. Unfortunately, the Linux driver needs to reset before initializing itself. At the moment, our default driver is not designed to have a proper transition between Uboot and Linux. If you remove the reset code, Kernel will hang. We are looking into the above request and I do not have any timelines.

Regards,

Krunal

Hi, Krunal：

        I have deleted dispc_softreset in the tidss_dispc.c driver and made changes in tidss_irq.c according to the reference you gave, the kernel will not hang.  

tidss_dispc.c:

for (i = 0; i < dispc->feat->num_planes; i++) {
r = dispc_iomap_resource(pdev, dispc->feat->vid_name[i],
&dispc->base_vid[i]);
if (r)
return r;
}

/* K2G display controller does not support soft reset */
//if (feat->subrev != DISPC_K2G)
//dispc_softreset(dispc);

for (i = 0; i < dispc->feat->num_vps; i++) {

tidss_irq.c:

static void tidss_irq_preinstall(struct drm_device *ddev)

{
struct tidss_device *tidss = to_tidss(ddev);

spin_lock_init(&tidss->wait_lock);

//tidss_runtime_get(tidss);

dispc_set_irqenable(tidss->dispc, 0);
dispc_read_and_clear_irqstatus(tidss->dispc);

//tidss_runtime_put(tidss);
}

static void tidss_irq_postinstall(struct drm_device *ddev)
{
struct tidss_device *tidss = to_tidss(ddev);
unsigned long flags;
unsigned int i;

//tidss_runtime_get(tidss);

spin_lock_irqsave(&tidss->wait_lock, flags);

tidss->irq_mask = DSS_IRQ_DEVICE_OCP_ERR;

for (i = 0; i < tidss->num_crtcs; ++i) {
struct tidss_crtc *tcrtc = to_tidss_crtc(tidss->crtcs[i]);

tidss->irq_mask |= DSS_IRQ_VP_SYNC_LOST(tcrtc->vp_idx);

tidss->irq_mask |= DSS_IRQ_VP_FRAME_DONE(tcrtc->vp_idx);
}

tidss_irq_update(tidss);

spin_unlock_irqrestore(&tidss->wait_lock, flags);

//tidss_runtime_put(tidss);
}

        We can determine that the framebuffer address is inconsistent.

        When I force the framebuffer address to be the same, the screen will not flicker(removed dispc_softreset). However, I am forcing the framebuffer setting of the register of the LCD controller. I don’t know how the framebuffer driver under the kernel can force the framebuffer address of the kernel and uboot to be the same. Otherwise, after application, the address written to the framebuffer first cannot correspond to the LCD controller register framebuffer settings.

Hello,

I am surprised your Kernel does not hang after few seconds with the above modifications because that was the behavior that I was observing. Anyways we currently do not have support for the above feature and our SW development team is looking into it.

Regards,

Krunal

Hi, Krunal:

        We use 24-Bit RGB LCD, which may be different from your application method. Check some information to display the logo smoothly under uboot and kernel. It is indeed necessary to achieve the same starting address of the framebuffer under uboot and kernel. Please consult your software team to see if there is a way to achieve this requirement. This is a very critical requirement in products using LCD.

Hello,

I am checking internally and will get back to you by the end of the week.

Regards,
Krunal

Hello,

Our dev team conducted the following experiment and had some success:

1. Make simple-framebuffer node using same fb address/properties as set in uboot (patch attached): 

2. Make simple-framebuffer region as reserved-area (this is already present in current codebase)

3. Enable simplefb in defconfig :

Hi Louis and Krunal,

Where do I have to set the framebuffer node in u-boot, so that the same framebuffer is used in kernel as well. The above framebuffer node you mentioned is for kernel dts. Does the u-boot dts will have same framebuffer node. Also in am625x SOC in uboot there are few CONFIGS related to simple framebuffer as shown below:

config VIDEO_SIMPLE
     bool "Simple display driver for preconfigured display"
     help
       Enables a simple generic display driver which utilizes the
       simple-framebuffer devicetree bindings.
 
       This driver assumes that the display hardware has been initialized
       before u-boot starts, and u-boot will simply render to the pre-
       allocated frame buffer surface.
 
 config VIDEO_DT_SIMPLEFB
     bool "Enable SimpleFB support for passing framebuffer to OS"
     help
       Enables the code to pass the framebuffer to the kernel as a
       simple framebuffer in the device tree.
       The video output is initialized by U-Boot, and kept by the
       kernel.

Do I need to enable them in u-boot defconfig.

For u-boot splash I followed this link

Also, I have enabled CONFIG_FB_SIMPLE in kernel defconfig. I need to know the framebuffer settings in u-boot

Also, I modified the drivers/video/logo/logo_linux_clut224.ppm file with my own file with the same name, and added CONFIG_LOGO_LINUX_CLUT224=y in kernel defconfig. Is this the correct approach or should i look into modifying the psplash which is present in yocto setup. 

Louis_Vertiv What was you approach for flicker free display from u-boot to kernel bootup. Please explain in detail

Thanks & Regards

Kamal