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SubjectRe: [PATCH v3 0/2] Add writeback scaling
On Tue, Apr 23, 2019 at 12:48 PM Ben Davis <Ben.Davis@arm.com> wrote:
>
> Add support for scaling on writeback. To do this add writeback_dest_w
> and writeback_dest_h as writeback connector properties to specify the
> desired output dimensions.
> Then implement downscaling on writeback for Malidp-550 and Malidp-650
> (upscaling on writeback is not supported on these devices).
>
> v2: Use 0 as default for writeback_w,h and so update range to use 1 as
> minimum.

Hm I missed that, I don't think that's good, since it prevents
userspace from blindly writing back the properties it's read. We've
tried hard to avoid that, since we're suggesting compositor can take a
snapshot of all kms properties (including the ones they don't
understand) and restore that on vt switching. Hence stuff like fence
fds returning -1, and accepting -1 as NULL to make this work.

tldr; I think range needs to include 0, and we need make that a
special thing, maybe enforced with a
drm_connector_state_compute_writeback_dst_h/w, which takes
crtc_state->mode.v/hdisplay into account if the writeback_dst_h/w is
0.
-Daniel

>
> v3: Rename properties to specify they are destination width/height.
> Make sure the values from the properties are passed to
> enable_memwrite rather than the framebuffer dimensions
>
> Ben Davis (2):
> drm: Add writeback_dest_w,h properties
> drm/malidp: Enable writeback scaling
>
> drivers/gpu/drm/arm/malidp_crtc.c | 49 +++++++++++---------
> drivers/gpu/drm/arm/malidp_crtc.h | 12 +++++
> drivers/gpu/drm/arm/malidp_drv.c | 10 +++--
> drivers/gpu/drm/arm/malidp_hw.c | 45 +++++++++++++------
> drivers/gpu/drm/arm/malidp_hw.h | 19 ++++++--
> drivers/gpu/drm/arm/malidp_mw.c | 94 ++++++++++++++++++++++++++++++---------
> drivers/gpu/drm/arm/malidp_regs.h | 1 +
> drivers/gpu/drm/drm_atomic_uapi.c | 8 ++++
> drivers/gpu/drm/drm_writeback.c | 30 +++++++++++++
> include/drm/drm_connector.h | 4 ++
> include/drm/drm_mode_config.h | 10 +++++
> 11 files changed, 220 insertions(+), 62 deletions(-)
> create mode 100644 drivers/gpu/drm/arm/malidp_crtc.h
>
> --
> 2.7.4
>


--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

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