linux-kernel - Re: [PATCH drm-misc-next v3 0/1] add drm_panic

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Message-ID: <aPEFs0kYfXGZUHCA@zeus>
Date: Thu, 16 Oct 2025 23:48:19 +0900
From: Ryosuke Yasuoka <ryasuoka@...hat.com>
To: zack.rusin@...adcom.com, maarten.lankhorst@...ux.intel.com,
	mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com,
	simona@...ll.ch, jfalempe@...hat.com, ian.forbes@...adcom.com
Cc: bcm-kernel-feedback-list@...adcom.com, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH drm-misc-next v3 0/1] add drm_panic_support for
 vmwgfx-stdu

On Fri, Sep 19, 2025 at 12:29:29PM +0900, Ryosuke Yasuoka wrote:
> Add drm_panic support for stdu in vmwgfx. This patch was tested in a VM
> with VMSVGA on Virtual Box.
> 
> Based on the feedback for v2 patch, I've made the following updates in
> my v3 patch.
> - Use MEMREMAP_WB | MEMREMAP_DEC flags for memremap
> - Use vmw_priv->initial_height and initial_width for sb and VRAM
> - Move all panic related functions to the vmwgfx_kms.c file
> - Ensure if the current display unit is 0 in get_scanout_buffer()
> 
> I did not apply all of Ian's feedback in this v3 patch for the reasons
> outlined below.
> 
> > 1. You can call `vmw_kms_write_svga` directly in `panic_flush`. There
> > is no need to mark the buffer as dirty or send any commands.
> 
> In my test environment (VirtualBox), the panic screen appears unstably 
> without dirty command's submission. Without it, the screen sometimes
> appears immediately as expected, and at other times, there's a delay
> of 15 to 20 seconds. I've also observed that it sometimes only appears
> after switching between the VirtualBox console window and other windows.
> 
> With command submission, we can stably get a panic screen. Even if it
> fails, we may get the panic screen ultimately. Therefore, I think we
> should retain vmw_kms_panic_do_bo_dirty() to submit commands.
> 
> > 2. The format should be hardcoded to RGB565 to minimize the risk of
> > overrunning VRAM. Adjust the pitch accordingly to 2x width.
> 
> While it's possible to output the panic screen with RGB565 by adjusting
> pitch and width, and BPP on the (virtual) hardware side, this approach
> causes debugfs to fail. It appears that the BPP must be reset after the
> panic screen is displayed, and there is no way to wait for the screen
> to be fully displayed within the drm_panic handler code.
> 
> In my test environment, as VRAM has enough space even when using
> XRGB8888 (32 bits), I think the risk of overruning VRAM is low. So I've
> kept the default format and CPP size.
> 
> v1:
> https://lore.kernel.org/all/20250901083701.32365-1-ryasuoka@redhat.com/
> 
> v2:
> https://lore.kernel.org/all/20250908141152.221291-2-ryasuoka@redhat.com/
> - Map a scanout_buffer to VRAM in .get_scanout_buffer
> - And then write to VRAM directly using fifo in legacy mode to avoid
> allocations or command submissions.
> 
> 
> Ryosuke Yasuoka (1):
>   drm/vmwgfx: add drm_panic support for stdu mode
> 
>  drivers/gpu/drm/vmwgfx/vmwgfx_drv.h  |   4 +
>  drivers/gpu/drm/vmwgfx/vmwgfx_kms.c  | 165 +++++++++++++++++++++++++++
>  drivers/gpu/drm/vmwgfx/vmwgfx_stdu.c |   2 +
>  3 files changed, 171 insertions(+)
> 
> 
> base-commit: d41c79838c47bc822534cd53628fe5e0f8ad2424
> -- 
> 2.51.0

Hi all,

This is a gentle reminder for this v3 patch.
I would appreciate any feedback when you have a chance.

Ian, your feedback on v1 and v2 were very helpful. I would appreciate it
if you could take another look when you have a moment.

Any comments are welcome.

Thank you
Ryosuke