Re: [PATCH 3/6] media: vsp1: dl: Use singleshot DL for VSPX

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Fri, Jan 24, 2025 at 09:44:06AM +0100, Jacopo Mondi wrote:
> Hi Laurent
> 
> On Thu, Jan 23, 2025 at 11:44:45PM +0200, Laurent Pinchart wrote:
> > Hi Jacopo,
> >
> > Thank you for the patch.
> >
> > On Thu, Jan 23, 2025 at 06:04:04PM +0100, Jacopo Mondi wrote:
> > > The vsp1_dl library allows to program a display list and feed it
> > > continuously to the VSP2. As an alternative operation mode, the library
> > > allows to program the VSP2 in 'single shot' mode, where a display list
> > > is submitted to the VSP on request only.
> > >
> > > Currently the 'single shot' mode is only available when the VSP2 is
> > > controlled by userspace, while it works in continuous mode when driven
> > > by DRM, as frames have to be submitted to the display continuously.
> > >
> > > For the VSPX use case, where there is no uapi support, we should however
> > > work in single-shot mode as the ISP driver programs the VSPX on
> > > request.
> > >
> > > Initialize the display lists in single shot mode in case the VSP1 is
> > > controlled by userspace or in case the pipeline features an IIF entity,
> > > as in the VSPX case.
> > >
> > > Signed-off-by: Jacopo Mondi <jacopo.mondi+renesas@ideasonboard.com>
> > > ---
> > >  drivers/media/platform/renesas/vsp1/vsp1_dl.c | 7 ++++++-
> > >  1 file changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/media/platform/renesas/vsp1/vsp1_dl.c b/drivers/media/platform/renesas/vsp1/vsp1_dl.c
> > > index ad3fa1c9cc737c92870c087dd7cb8cf584fce41b..b8f0398522257f2fb771b419f34b56e59707476b 100644
> > > --- a/drivers/media/platform/renesas/vsp1/vsp1_dl.c
> > > +++ b/drivers/media/platform/renesas/vsp1/vsp1_dl.c
> > > @@ -1099,7 +1099,12 @@ struct vsp1_dl_manager *vsp1_dlm_create(struct vsp1_device *vsp1,
> > >  		return NULL;
> > >
> > >  	dlm->index = index;
> > > -	dlm->singleshot = vsp1->info->uapi;
> > > +	/*
> > > +	 * uapi = single shot mode;
> > > +	 * DRM = continuous mode;
> > > +	 * VSPX = single shot mode;
> > > +	 */
> > > +	dlm->singleshot = (vsp1->info->uapi || vsp1->iif);
> >
> > I'm wondering if we should make this a bit more generic, and allow the
> > caller to select the mode of operation. It could be passed as a flag to
> > vsp1_dl_list_commit() and stored in the vsp1_dl_list.
> >
> > There is however no use case at the moment to switch between singleshot
> > and continuous modes on a per display list basis. Implementing support
> > for that may be overkill, but on the other hand, the implementation
> > seems very simple, so it's not a big effort. The main and possibly only
> > reason why we may not want to do that now is because the display list
> > helpers haven't been tested to successfully switch between the modes, so
> > we may falsely advertise something as supported. Despite that, as no
> > caller would attempt switching, it wouldn't cause an issue.
> 
> I would simply avoid upstreaming code I can't test, and changing the
> singleshot mode between commit might create contentions with
> vsp1_dlm_irq_frame_end() which inspects dlm->singleshot.

I had considered that when looking at the code. Moving the single shot
flag to the vsp1_dl_list, vsp1_dlm_irq_frame_end() would check the flag
from that structure instead of getting it from the dlm, so I don't think
it would be an issue. That's the reason why I'm in two minds about this,
I think it would be easy to do, with very low risk for our use cases,
but indeed the switch itself wouldn't be fully tested.

> > What do you think ? What do you feel would be cleaner ?
> >
> > >  	dlm->vsp1 = vsp1;
> > >
> > >  	spin_lock_init(&dlm->lock);

-- 
Regards,

Laurent Pinchart