[v2,3/8] firmware/sysfb: Set firmware-framebuffer parent device

[Sui Jingfeng]

Hi,


On 2024/2/5 16:24, Thomas Zimmermann wrote:
> Hi
>
> Am 02.02.24 um 16:23 schrieb Sui Jingfeng:
>> Hi,
>>
>>
>> On 2024/2/2 19:58, Thomas Zimmermann wrote:
>>> Set the firmware framebuffer's parent device, which usually is the
>>> graphics hardware's physical device. Integrates the framebuffer in
>>> the Linux device hierarchy and lets Linux handle dependencies among
>>> devices. For example, the graphics hardware won't be suspended while
>>> the firmware device is still active.
>>
>> This is a very nice benefit, I can't agree more!
>>
>> Because the backing memory of the firmware framebuffer occupied
>> belongs to the graphics hardware itself. For PCIe device, the
>> backing memory is typically the dedicated VRAM of the PCIe GPU.
>> But there are some exceptions, for example, the gma500. But I
>> think this can be fixed in the future, as majority(>99.9%) PCIe
>> GPU has the a dedicated VRAM.
>>
>>
>> For ARM and ARM64 platform device, the backing memory of the
>> firmware framebuffer may located at the system RAM. It's common
>> that the display controller is a platform device in the embedded
>> world. So I think the sysfb_parent_dev() function can be extended
>> to be able to works for platform device in the future.
>
> The current approach has been taken from efifb. It would already not 
> work reliably with gma500 or ARM SoCs. So there's no immediate loss of 
> functionality AFAICT. But with the patchset now have a correct device 
> hierarchy and PM for simpledrm, vesafb et al.
>
> In the long term, I want to employ some of the logic in vgaarb that 
> detects the firmware default device. That needs additional work, though.
>

Good ideas, try to be impressive.
I probably could help to test if I'm online.


> Best regards
> Thomas
>
>>
>