drm_gem_dumb_map_offset patch

[Noralf Trønnes]

Hi,

[add Daniel Vetter]
[cc dri-devel]

Den 29.05.2019 15.09, skrev Pierre Yves MORDRET:
> Hello Noralf,
> 
> Sorry for bothering you with question but I need to better understand the
> rational about a patch you did in DRM/GEM.
> 
> First of all, let me introduce myself.
> I'm currently employee to STMicroelectronics company and in charge of GPU
> integration within STM32 MPU (Cortex A7 + Cortex M4)
> 
> On Cortex A7 is running a Linux Kernel 4.19 as for today.
> 
> We came across some trouble when we switch from Kernel 4.14 to 4.19 for GPU
> stack. On august you submit this commit :
> 
> 	90378e58919285637aa0f063c04ba0c6449d98b1
>     	    drm/gem: drm_gem_dumb_map_offset(): reject dma-buf
> 
>     	    Reject mapping an imported dma-buf since is's an invalid use-case.
> 
> In Userland GPU stack we have such statements :
>    bo_map_fd
>        DRM_IOCTL_MODE_MAP_DUMB
>        mmap (offset)
> 
> With the patch above, ioctl returns an error EINVAL and prevents the nmap.
> As for today we revert this patch and it works fine in our end.
> 
> Thus the questions are :
>  - what is the rational behind this fix ?
>  - What we doing wrong this situation ?
>  - What do we need in such situation ?
> 

I need to pass those on to Daniel Vetter (DRM maintainer) since he
wanted the change. The details were never clear to me.
Some of the discussion is here:
https://patchwork.freedesktop.org/patch/172242/

Noralf.

> Many thanks in advance.
> Best Regards
>