Re: Reuse framebuffer after a kexec (amdgpu / efifb)

From: "Guilherme G. Piccoli" <gpiccoli@igalia.com>
To: Alex Deucher <alexdeucher@gmail.com>
Cc: "open list:EFIFB FRAMEBUFFER DRIVER"
	<linux-fbdev@vger.kernel.org>, "xinhui pan" <Xinhui.Pan@amd.com>,
	kasong@redhat.com, "Baoquan He" <bhe@redhat.com>,
	"Samuel Iglesias Gonsálvez" <siglesias@igalia.com>,
	kernel@gpiccoli.net, kexec@lists.infradead.org,
	"amd-gfx list" <amd-gfx@lists.freedesktop.org>,
	pjones@redhat.com,
	"Maling list - DRI developers" <dri-devel@lists.freedesktop.org>,
	"Deucher, Alexander" <alexander.deucher@amd.com>,
	"Dave Young" <dyoung@redhat.com>,
	"Christian Koenig" <christian.koenig@amd.com>,
	"Vivek Goyal" <vgoyal@redhat.com>,
	"Gerd Hoffmann" <kraxel@redhat.com>
Subject: Re: Reuse framebuffer after a kexec (amdgpu / efifb)
Date: Thu, 9 Dec 2021 14:59:52 -0300	[thread overview]
Message-ID: <a1f4d263-b3d2-4ceb-8a89-948c8129500f@igalia.com> (raw)
In-Reply-To: <CADnq5_O8x3_8f7GZ=tme55-QW+nqMJ2YoqvROjDPg2YZP2catQ@mail.gmail.com>

On 09/12/2021 14:31, Alex Deucher wrote:
> [...] 
> Once the driver takes over, none of the pre-driver state is retained.
> You'll need to load the driver in the new kernel to initialize the
> displays.  Note the efifb doesn't actually have the ability to program
> any hardware, it just takes over the memory region that was used for
> the pre-OS framebuffer and whatever display timing was set up by the
> GOP driver prior to the OS loading.  Once that OS driver has loaded
> the area is gone and the display configuration may have changed.
> 

Hi Christian and Alex, thanks for the clarifications!

Is there any way to save/retain this state before amdgpu takes over?
Would simpledrm be able to program the device again, to a working state?

Finally, do you have any example of such a GOP driver (open source) so I
can take a look? I tried to find something like that in Tianocore
project, but didn't find anything that seemed useful for my issue.

Thanks again!