Re: [PATCH v3 3/5] drm/rockchip: Add optional support for CRTC gamma LUT

[Ezequiel Garcia <ezequiel@collabora.com>]

On Tue, 2019-10-08 at 16:23 -0300, Ezequiel Garcia wrote:
> Hello Sean,
> 
> On Mon, 2019-10-07 at 14:54 -0400, Sean Paul wrote:
> > On Mon, Sep 30, 2019 at 07:28:00PM -0300, Ezequiel Garcia wrote:
> > > Add an optional CRTC gamma LUT support, and enable it on RK3288.
> > > This is currently enabled via a separate address resource,
> > > which needs to be specified in the devicetree.
> > > 
> > > The address resource is required because on some SoCs, such as
> > > RK3288, the LUT address is after the MMU address, and the latter
> > > is supported by a different driver. This prevents the DRM driver
> > > from requesting an entire register space.
> > > 
> > > The current implementation works for RGB 10-bit tables, as that
> > > is what seems to work on RK3288.
> > > 
> > > Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
> > > Reviewed-by: Douglas Anderson <dianders@chromium.org>
> > > Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> > > ---
> > > Changes from v2:
> > > * None.
> > > 
> > > Changes from v1:
> > > * drop explicit linear LUT after finding a proper
> > >   way to disable gamma correction.
> > > * avoid setting gamma is the CRTC is not active.
> > > * s/int/unsigned int as suggested by Jacopo.
> > > * only enable color management and set gamma size
> > >   if gamma LUT is supported, suggested by Doug.
> > > * drop the reg-names usage, and instead just use indexed reg
> > >   specifiers, suggested by Doug.
> > > 
> > > Changes from RFC:
> > > * Request (an optional) address resource for the LUT.
> > > * Drop support for RK3399, which doesn't seem to work
> > >   out of the box and needs more research.
> > > * Support pass-thru setting when GAMMA_LUT is NULL.
> > > * Add a check for the gamma size, as suggested by Ilia.
> > > * Move gamma setting to atomic_commit_tail, as pointed
> > >   out by Jacopo/Laurent, is the correct way.
> > > ---
> > >  drivers/gpu/drm/rockchip/rockchip_drm_fb.c  |   3 +
> > >  drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 114 ++++++++++++++++++++
> > >  drivers/gpu/drm/rockchip/rockchip_drm_vop.h |   7 ++
> > >  drivers/gpu/drm/rockchip/rockchip_vop_reg.c |   2 +
> > >  4 files changed, 126 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> > > index dba352ec0ee3..fd1d987698ab 100644
> > > --- a/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> > > +++ b/drivers/gpu/drm/rockchip/rockchip_drm_fb.c
> > > @@ -17,6 +17,7 @@
> > >  #include "rockchip_drm_drv.h"
> > >  #include "rockchip_drm_fb.h"
> > >  #include "rockchip_drm_gem.h"
> > > +#include "rockchip_drm_vop.h"
> > >  
> > >  static const struct drm_framebuffer_funcs rockchip_drm_fb_funcs = {
> > >  	.destroy       = drm_gem_fb_destroy,
> > > @@ -112,6 +113,8 @@ rockchip_atomic_helper_commit_tail_rpm(struct drm_atomic_state *old_state)
> > >  
> > >  	drm_atomic_helper_commit_modeset_disables(dev, old_state);
> > >  
> > > +	rockchip_drm_vop_gamma_set(old_state);
> > > +
> > 
> > Instead of duplicating the commit_tail helper, could you just implement
> > .atomic_begin() and call this from there? I think the only hitch is if you
> > need this to be completed before crtc->atomic_enable(), at which point you
> > might need to call it from vop_crtc_atomic_enable() and then detect that in
> > atomic_begin()
> > 
> 
> I think moving this to .atomic_begin might be enough. Let me send a new
> series and we can see how that goes.
> 

Oh, before going forward, pleaste note that the first iteration
of this patch (as noted in the changelog) was applying the gamma lut
on .atomic_flush. However, Laurent and Jacopo pointed out that
it might add some tearing to do so, and that's why it was moved
to commit_tail.

I have to admit I'm not too sure about the difference between
applying this gamma LUT on atomic_begin or atomic_flush,
perhaps you can clarify that?

Thanks!
Ezequiel