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

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Message-ID: <CAO6MGtj5LCKBJfTETPb_dUBSVO3de8hZLUMSm5thyeMeY8bEXw@mail.gmail.com>
Date: Thu, 23 Oct 2025 15:12:38 -0500
From: Ian Forbes <ian.forbes@...adcom.com>
To: Ryosuke Yasuoka <ryasuoka@...hat.com>
Cc: zack.rusin@...adcom.com, maarten.lankhorst@...ux.intel.com, 
	mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com, simona@...ll.ch, 
	jfalempe@...hat.com, 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

If it doesn't work on vbox that's not really our problem. I've sent my
version [1] that works on Workstation and ESXI.
Since it has less code it has a much higher chance of succeeding in a
panic situation which is what we care about.
Feel free to add whatever tags you feel are appropriate on that patch review.

[1] https://lore.kernel.org/dri-devel/20251023200447.206834-1-ian.forbes@broadcom.com/T/#u

Ian,

On Thu, Oct 16, 2025 at 9:48 AM Ryosuke Yasuoka <ryasuoka@...hat.com> wrote:
>
> 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
>

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