Re: drm/loongson: Error out if no VRAM detected

[Katyusha <KatyushaScarlet@xxxxxxxxxxx>]

Hi,

This patch works fine with my Loongson 3A5000M laptop (L71), which has a 7A1000 chipset without VRAM.

On 2024/1/20 0:18, Sui JIngfeng wrote:

> Hi,
>       
>       
>       Thanks a lot for contribution.
>       
>       
>       On 2024/1/19 18:40, Huacai Chen wrote:
>       
> > If there is no VRAM (it is true if there
> >         is a discreted card),
> >         
> >       
>       
>       
>       Why the dedicated VRAM is gone whenthere is a discrete card?
>       
>       
>       As far as I know, this is only possible on Loongson 3C5000 +
>       aspeed BMC server hardware platform where the dedicated VRAM chip
>       of Loongson Graphics is NOT soldered on the motherboard. Probably
>       for cost reason, but then, the platform BIOS(either UEFI or PMON)
>       should turn off the Loongson integrated graphics.
>       
>       
>       Because without dedicated VRAM, this driver can not work
>       correctly. Or carve out
>       
>       part of system RAM as VRAM, and write the base address and size to
>       the BAR 2 of
>       
>       the GPU PCI device.
>       
>       This is NOT true  for Loongson 3A5000/3A6000  desktop hardware,
>       because I have do
>       
>       a lot test on various platform[1] before this driver was merged.
>       It never happens
>       
>       on a sane hardware configuration. Please update the commit message
>       and limit the
>       
>       scope.
>       
>       
>       [1] https://github.com/loongson-gfx/loongson_boards
>       
>       
> > we get
> >         
> >         such an error and Xorg fails to start:
> >         
> >       
>       
>       
>       Yeah, If there is no dedicated VRAM, the driver can't allocate
>       memory for framebuffer.
>       
>       But this is probably more about the hardware configuration issue,
>       not a driver issue.
>       
>       
>       
> > [  136.401131] loongson 0000:00:06.1:
> >         [drm] *ERROR* Requesting(0MiB) failed
> >         
> >         [  137.444342] loongson 0000:00:06.1: [drm] *ERROR*
> >         Requesting(0MiB) failed
> >         
> >         [  138.871166] loongson 0000:00:06.1: [drm] *ERROR*
> >         Requesting(0MiB) failed
> >         
> >         [  140.444078] loongson 0000:00:06.1: [drm] *ERROR*
> >         Requesting(0MiB) failed
> >         
> >         [  142.403993] loongson 0000:00:06.1: [drm] *ERROR*
> >         Requesting(0MiB) failed
> >         
> >         [  143.970625] loongson 0000:00:06.1: [drm] *ERROR*
> >         Requesting(0MiB) failed
> >         
> >         [  145.862013] loongson 0000:00:06.1: [drm] *ERROR*
> >         Requesting(0MiB) failed
> >         
> >         
> >         So in lsdc_get_dedicated_vram() we error out if no VRAM (or VRAM
> >         is less
> >         
> >         than 1MB which is also an unusable case) detected.
> >         
> >       
>       
>       
>       This is not expected, if you want this driver be there and run
>       normally.
>       
>       You should guarantee that there have at least 64MiB dedicated
>       VRAM.
>       
>       
>       I'm OK if this patch is strongly requested, but this is a kind of
>       error handling.
>       
>       Please give more details about the hardware in using and explain
>       why there is no
>       
>       dedicated VRAM available for your hardware.
>       
>       
>       
> > Signed-off-by: Huacai Chen
> >         <chenhuacai@xxxxxxxxxxx>
> >         
> >         ---
> >         
> >           drivers/gpu/drm/loongson/lsdc_drv.c | 2 +-
> >         
> >           1 file changed, 1 insertion(+), 1 deletion(-)
> >         
> >         
> >         diff --git a/drivers/gpu/drm/loongson/lsdc_drv.c
> >         b/drivers/gpu/drm/loongson/lsdc_drv.c
> >         
> >         index 89ccc0c43169..d8ff60b46abe 100644
> >         
> >         --- a/drivers/gpu/drm/loongson/lsdc_drv.c
> >         
> >         +++ b/drivers/gpu/drm/loongson/lsdc_drv.c
> >         
> >         @@ -184,7 +184,7 @@ static int lsdc_get_dedicated_vram(struct
> >         lsdc_device *ldev,
> >         
> >               drm_info(ddev, "Dedicated vram start: 0x%llx, size:
> >         %uMiB\n",
> >         
> >                    (u64)base, (u32)(size >> 20));
> >         
> >           -    return 0;
> >         
> >         +    return (size > SZ_1M) ? 0 : -ENODEV;
> >         
> >           }
> >         
> >             static struct lsdc_device *
> >         
> >       
>       
>