On 2023/6/10 00:48, Bjorn Helgaas wrote:
On Fri, Jun 09, 2023 at 10:27:39AM +0800, Sui Jingfeng wrote:
On 2023/6/9 03:19, Bjorn Helgaas wrote:
On Thu, Jun 08, 2023 at 07:43:22PM +0800, Sui Jingfeng wrote:
From: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
The vga_is_firmware_default() function is arch-dependent, which doesn't
sound right. At least, it also works on the Mips and LoongArch platforms.
Tested with the drm/amdgpu and drm/radeon drivers. However, it's difficult
to enumerate all arch-driver combinations. I'm wrong if there is only one
exception.
With the observation that device drivers typically have better knowledge
about which PCI bar contains the firmware framebuffer, which could avoid
the need to iterate all of the PCI BARs.
But as a PCI function at pci/vgaarb.c, vga_is_firmware_default() is
probably not suitable to make such an optimization for a specific device.
There are PCI display controllers that don't have a dedicated VRAM bar,
this function will lose its effectiveness in such a case. Luckily, the
device driver can provide an accurate workaround.
Therefore, this patch introduces a callback that allows the device driver
to tell the VGAARB if the device is the default boot device. This patch
only intends to introduce the mechanism, while the implementation is left
to the device driver authors. Also honor the comment: "Clients have two
callback mechanisms they can use"
s/bar/BAR/ (several)
Nothing here uses the callback. I don't want to merge this until we
have a user.
This is chicken and egg question.
If you could help get this merge first, I will show you the first user.
I'm not sure why the device driver should know whether its device is
the default boot device.
It's not that the device driver should know,
but it's about that the device driver has the right to override.
Device driver may have better approach to identify the default boot
device.
The way we usually handle this is to include the new callback in the
same series as the first user of it. That has two benefits:
(1) everybody can review the whole picture and possibly suggest
different approaches, and (2) when we merge the infrastructure,
we also merge a user of it at the same time, so the whole thing can be
tested and we don't end up with unused code.
OK, acceptable
I will try to prepare the user code of this callback and respin the patch.
I may resend it with another patch set in the future, this series
already drop it,
see v5[1]
[1] https://patchwork.freedesktop.org/series/119134/
Bjorn
