[bug report] drm/nouveau/gsp: add hal for gsp.get_static_info()

[Timur Tabi]

On Fri, 2025-05-23 at 19:03 +0300, Dan Carpenter wrote:
> [ Did these files get renamed or something?  No idea why the warnings
>   are showing up as new now. ]

Ben posted a large refactor of the code last week.

> Hello Ben Skeggs,
> 
> Commit 7bb77eacdb85 ("drm/nouveau/gsp: add hal for
> gsp.get_static_info()") from Nov 14, 2024 (linux-next), leads to the
> following Smatch static checker warning:
> 
> drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/ctrl.c:47 r535_gsp_rpc_rm_ctrl_push() warn:
> passing zero to 'PTR_ERR'
> drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/gsp.c:223 r535_gsp_get_static_info() warn: 'rpc'
> can also be NULL
> drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r570/gsp.c:90 r570_gsp_get_static_info() warn: 'rpc'
> can also be NULL
> 
> drivers/gpu/drm/nouveau/nvkm/subdev/gsp/rm/r535/gsp.c
>     212 static int
>     213 r535_gsp_get_static_info(struct nvkm_gsp *gsp)
>     214 {
>     215         GspStaticConfigInfo *rpc;
>     216 
>     217         rpc = nvkm_gsp_rpc_rd(gsp, NV_VGPU_MSG_FUNCTION_GET_GSP_STATIC_INFO,
> sizeof(*rpc));
>     218         if (IS_ERR(rpc))
>     219                 return PTR_ERR(rpc);
>     220 
>     221         gsp->internal.client.object.client = &gsp->internal.client;
>     222         gsp->internal.client.object.parent = NULL;
> --> 223         gsp->internal.client.object.handle = rpc->hInternalClient;
>                                                      ^^^^^
> 
> The nvkm_gsp_rpc_rd() function returns a mix of error pointers and NULL but
> if it returns NULL then obviously this dereference will crash.
> 
> https://staticthinking.wordpress.com/2022/08/01/mixing-error-pointers-and-null/

Well, there's definitely something weird going on with this code.  It appears that nvkm_gsp_rpc_rd()
actually returns NULL on success.  

	nvkm_gsp_rpc_rd -> r535_gsp_rpc_push -> r535_gsp_rpc_handle_reply()

So either I'm confused, or this will need further debugging.