drm/loongson: Error out if no VRAM detected

[Sui JIngfeng]

Hi,


On 2024/1/21 00:07, yetist wrote:
> Without this patch, my server cannot start the DM. It is a Loongson 
> 3C5000L server, with both a Loongson display controller and an ASPEED 
> graphics card.
>
>   $ lspci |grep VGA
>   0000:00:06.1 VGA Compatible Controller: Loongson Technology LLC DC 
> (Display Controller) (rev 01)
>   0000:03:00.0 VGA-compatible controller: ASPEED Technology, Inc. 
> ASPEED Graphics Family (revision 41)
>
> When not working, there is the following information in dmesg:
>
>   loongson 0000:00:06.1: [drm] Private vram start: 0xe00472a6000, 
> size: 0MiB
>   Loongson 0000:00:06.1: [drm] *Error* Request (0MiB) failed
>
>
> Anyway, this patch works fine with my server now, thank you.
>

Does the sever you are using has a dedicated VRAM for the 0000:00:06.1?

If not, the driver shouldn't be probed. This also means that the 0000:00:06.1
(Display Controller) shouldn't be detected by Linux kernel, because there is
no way for this driver can works correctly on such a case.