Re: [PATCH] drm/msm: enable separate_gpu_kms by default

[Rob Clark]

On Tue, Mar 3, 2026 at 2:32 PM Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxxxxxxxx> wrote:
>
> On Tue, Mar 03, 2026 at 10:35:46AM -0800, Rob Clark wrote:
> > On Sun, Feb 22, 2026 at 12:32 PM Dmitry Baryshkov
> > <dmitry.baryshkov@xxxxxxxxxxxxxxxx> wrote:
> > >
> > > On Mon, Feb 23, 2026 at 12:40:10AM +0530, Mahadevan P wrote:
> > > > On targets with multiple display subsystems, such as SA8775P, the GPU
> > > > binds to the first display subsystem that probes. This implicit binding
> > > > prevents subsequent display subsystems from probing successfully,
> > > > breaking multi-display support.
> > > >
> > > > Enable separate_gpu_kms by default to decouple GPU and display subsystem
> > > > probing. This allows each display subsystem to initialize independently,
> > > > ensuring that all display subsystems are probed.
> > > >
> > > > Signed-off-by: Mahadevan P <mahadevan.p@xxxxxxxxxxxxxxxx>
> > > > ---
> > > > Depends on:
> > > >       https://lore.kernel.org/lkml/20260124-adreno-module-table-v1-1-9c2dbb2638b4@xxxxxxxxxxxxxxxx/
> > > >       https://lore.kernel.org/all/20260217071420.2240380-1-mkuntuma@xxxxxxxxxxxxxxxx/
> > >
> > > What exactly depends on this patchset?
> > >
> > > > ---
> > > >  drivers/gpu/drm/msm/msm_drv.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> > > > index ed2a61c66ac9..65119fb3dfa2 100644
> > > > --- a/drivers/gpu/drm/msm/msm_drv.c
> > > > +++ b/drivers/gpu/drm/msm/msm_drv.c
> > > > @@ -54,7 +54,7 @@ static bool modeset = true;
> > > >  MODULE_PARM_DESC(modeset, "Use kernel modesetting [KMS] (1=on (default), 0=disable)");
> > > >  module_param(modeset, bool, 0600);
> > > >
> > > > -static bool separate_gpu_kms;
> > > > +static bool separate_gpu_kms = true;
> > > >  MODULE_PARM_DESC(separate_gpu_drm, "Use separate DRM device for the GPU (0=single DRM device for both GPU and display (default), 1=two DRM devices)");
> > > >  module_param(separate_gpu_kms, bool, 0400);
> > >
> > > The patch LGTM, but I'd prefer to get confirmation from Rob.
> >
> > I prefer to be a bit more paranoid.. perhaps switch this to a tri-state:
> >
> >  -1: separate drm devices if there is more than one dpu or gpu,
> >      otherwise, single combined drm device [default]
> >   0: single drm device (matching up pairs of dpu and gpu if needed)
> >   1: separate drm devices
> >
> > This way we aren't changing (or breaking) things for existing users.
>
> I'd rather break things and hear about them being broken.

You are assuming you'd hear about the non-obvious breakages
immediately..  I don't think that is a good assumption.

To be clear, I'll NAK any change to the default for "normal" hw
configurations.  If you want to change the modparam to tri-state so
that "weird" hw configurations get split devices, I guess I'd be ok
with that.  At least it limits the potential fallout.

BR,
-R

> >
> > BR,
> > -R
> >
> > > BTW: have you tested it with X11? Are you still getting accelerated GPU?
> > >
> > > --
> > > With best wishes
> > > Dmitry
>
> --
> With best wishes
> Dmitry