Nouveau - Sep 2023 - [RFC, drm-misc-next v4 0/9] PCI/VGA: Allowing the user to select the primary video adapter at boot time

Am 06.09.23 um 11:08 schrieb suijingfeng:
> Well, welcome to correct me if I'm wrong.
You seem to have some very basic misunderstandings here.

The term framebuffer describes some VRAM memory used for scanout.

This framebuffer is exposed to userspace through some framebuffer 
driver, on UEFI platforms that is usually efifb but can be quite a bunch 
of different drivers.

When the DRM drivers load they remove the previous drivers using 
drm_aperture_remove_conflicting_pci_framebuffers() (or similar 
function), but this does not mean that the framebuffer or scanout 
parameters are modified in any way. It just means that the framebuffer 
is just no longer exposed through this driver.

Take over is the perfectly right description here because that's exactly 
what's happening. The framebuffer configuration including the VRAM 
memory as well as the parameters for scanout are exposed by the newly 
loaded DRM driver.

In other words userspace can query through the DRM interfaces which 
monitors already driven by the hardware and so in your terminology 
figure out which is the primary one.

It's just that as Thomas explained as well that this completely 
irrelevant to any modern desktop. Both X and Wayland both iterate the 
available devices and start rendering to them which one was used during 
boot doesn't really matter to them.

Apart from that ranting like this and trying to explain stuff to people 
who obviously have much better background in the topic is not going to 
help your patches getting upstream.

Regards,
Christian.

Hi,


On 2023/9/6 17:40, Christian K?nig wrote:
> Am 06.09.23 um 11:08 schrieb suijingfeng:
>> Well, welcome to correct me if I'm wrong.
>
> You seem to have some very basic misunderstandings here.
>
> The term framebuffer describes some VRAM memory used for scanout.
>
> This framebuffer is exposed to userspace through some framebuffer 
> driver, on UEFI platforms that is usually efifb but can be quite a 
> bunch of different drivers.
>
> When the DRM drivers load they remove the previous drivers using 
> drm_aperture_remove_conflicting_pci_framebuffers() (or similar 
> function), but this does not mean that the framebuffer or scanout 
> parameters are modified in any way. It just means that the framebuffer 
> is just no longer exposed through this driver.
>
> Take over is the perfectly right description here because that's 
> exactly what's happening. The framebuffer configuration including the 
> VRAM memory as well as the parameters for scanout are exposed by the 
> newly loaded DRM driver.
>
> In other words userspace can query through the DRM interfaces which 
> monitors already driven by the hardware and so in your terminology 
> figure out which is the primary one.
>
I'm a little bit of not convinced about this?idea,?you might be correct.
But there cases where three are multiple monitors and each video card
connect one.

It also quite common that no monitors is connected, let the machine boot
first, then find a monitors to connect to a random display output. See
which will display. I don't expect the primary shake with.
The primary one have to be determined as early as possible, because of
the VGA console and the framebuffer console may directly output the primary.
Get the DDC and/or HPD involved may necessary complicated the problem.

There are ASpeed BMC who add a virtual connector in order to able display
remotely.
There are also have commands to force a connector to be connected status.

> It's just that as Thomas explained as well that this completely 
> irrelevant to any modern desktop. Both X and Wayland both iterate the 
> available devices and start rendering to them which one was used 
> during boot doesn't really matter to them.
>
You may be correct, but I'm still not sure.
I probably need more times to investigate.
Me and my colleagues are mainly using X server,
the version varies from 1.20.4 and 1.21.1.4.
Even this is true, the problems still exist for non-modern desktops.
> Apart from that ranting like this and trying to explain stuff to 
> people who obviously have much better background in the topic is not 
> going to help your patches getting upstream.
>
Thanks for you tell me so much knowledge,
I'm realized where are the problems now.
I will try to resolve the concerns at the next version.

> Regards,
> Christian.
>