Re: [PATCH v1 06/11] FSF: hardware: graphics-card: Nvidia: Warn about nonfree software.

[Denis 'GNUtoo' Carikli]

Hi,

On Tue,  5 Nov 2024 15:14:28 +0100
Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org> wrote:
> -<https://nouveau.freedesktop.org/CodeNames.html>
> +Nvidia graphics card or chip require nonfree software to work:
> +
> +  * If the display works during the boot (in GRUB for instance) it
> +    means that the boot software (the BIOS/UEFI, etc) ran the nonfree
> +    video BIOS that is stored on a memory chip inside the graphic
> card. +
> +  * The nvidia driver need to load and run some bytecode that is also
> +    stored somewhere in the memory chip of the graphic card.
> +
> +Beside the video BIOS issue, another question is if these cards works
> +in free distros.

After some discussion on the topic with neox, the second bullet point
may not be true 100% of the time: we didn't verify yet that the driver
code that loads and run this nonfree code runs in all the cases (it
might only run on laptops for instance).

So I propose the following instead:
> -<https://nouveau.freedesktop.org/CodeNames.html>
> +Nvidia graphics card often uses nonfree software to work: If the
> +display works during the boot (in GRUB for instance) it means that
> the +boot software (the BIOS/UEFI, etc) ran the nonfree video BIOS
> that is +stored on a memory chip inside the graphic card.
> +
> +The nouveau driver also has code that loads and run some nonfree code
> +that is stored inside the same memory chip inside the graphic card.
> We +don't know yet the precise conditions in which this code is run
> +(someone would need to do very simple modifications to the driver to
> +find out and review a bit the driver code) so we don't know yet if
> +it's possible to use these GPU with 100% free software or not
> +(assuming the boot software is configured not to run the nonfree
> video +BIOS).
> +
> +Beside these two issues, another question is if these cards works in
> +free distros.
> +
> +See <https://nouveau.freedesktop.org/CodeNames.html> for how to
> +identify the family of an Nvidia card.

For the people interested I've added more details on the second issue
below.

More details on the issue (optional):
-------------------------------------

In the nouveau driver we have this code in
drivers/gpu/drm/nouveau/nvkm/subdev/bios/init.c :

> int             
> nvbios_exec(struct nvbios_init *init)
> {                       
>         struct nvkm_bios *bios = init->subdev->device->bios;
>          
>         init->nested++;
>         while (init->offset) {
>                 u8 opcode = nvbios_rd08(bios, init->offset);
>                 if (opcode >= ARRAY_SIZE(init_opcode) ||
>                     !init_opcode[opcode].exec) {
>                         error("unknown opcode 0x%02x\n", opcode);
>                         return -EINVAL;
>                 }
>  
>                 init_opcode[opcode].exec(init);
>         }
>         init->nested--;
>         return 0;
> }

The nonfree instructions (opcodes) come from a zone inside the video
BIOS.

Inside nouveau we have the following function
calls: run_digital_op_script -> nouveau_bios_run_init_table ->
nvbios_init (drivers/gpu/drm/nouveau/dispnv04/disp.h) -> nvbios_exec
(nvkm/subdev/bios/init.c)

The run_digital_op_script is however called in 3 functions:
call_lvds_manufacturer_script, run_lvds_table and run_tmds_table.

LVDS is a display connector like HDMI or VGA that is found in laptops
(it's for the internal screen). TMDS seems somewhat similar to LVDS but
I never heard of it before so I've no idea if it's used in laptops or
not or if it's a synonym to HDMI or DVI in this context.

So the nonfree code most probably run on laptops but we have no
idea if it also runs with a KGPE-D16 and a GPU card. Someone needs to
replace the nvbios_exec function with prints and see if it works fine,
or if the function is called.

If these card can work without nonfree software, it would remove a huge
limitation of 100% free software as we would be able to build desktop
computers that run 100% free software and that are not limited to
server use cases or limited desktop usage (no multi-display).

Though without a free replacement for the video BIOS this would still be
extremely inconvenient to use on mainboards that don't already have
builtin display controller like the KGPE-D16.

In the case of the KGPE-D16 both the builtin display controller and
the nouveau GPU card can be wired to a display with multiple inputs
(like VGA and HDMI) for a very convenient that allows to see why the
computer isn't booting.

Denis.

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