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Fri, 19 Dec 2025 23:33:39 +0100 (CET) Message-ID: <7fb25158-5053-43d9-99df-59cab371d746@collabora.com> Date: Sat, 20 Dec 2025 00:33:39 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/4] drm/rockchip: vop2: Support setting custom background color From: Cristian Ciocaltea To: Chaoyi Chen , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Sandy Huang , =?UTF-8?Q?Heiko_St=C3=BCbner?= , Andy Yan , Louis Chauvet , Haneen Mohammed , Melissa Wen Cc: Robert Mader , kernel@collabora.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rockchip@lists.infradead.org References: <20251118-rk3588-bgcolor-v3-0-a2cc909428ea@collabora.com> <20251118-rk3588-bgcolor-v3-4-a2cc909428ea@collabora.com> <0ed71b8d-5a2e-4213-bd2f-7ba317d1e4cb@rock-chips.com> <4a6443b8-d440-4921-8a43-7c20e4e265e7@collabora.com> Content-Language: en-US In-Reply-To: <4a6443b8-d440-4921-8a43-7c20e4e265e7@collabora.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/28/25 11:44 AM, Cristian Ciocaltea wrote: > Hi Chaoyi, > > On 11/28/25 10:46 AM, Chaoyi Chen wrote: >> Hello Cristian, >> >> On 11/18/2025 7:52 AM, Cristian Ciocaltea wrote: >>> The Rockchip VOP2 display controller allows configuring the background >>> color of each video output port. >>> >>> Since a previous patch introduced the BACKGROUND_COLOR CRTC property, >>> which defaults to solid black, make use of it when programming the >>> hardware. >>> >>> Note the maximum precision allowed by the display controller is 10bpc, >>> while the alpha component is not supported, hence ignored. >>> >>> Signed-off-by: Cristian Ciocaltea >>> --- >>> drivers/gpu/drm/rockchip/rockchip_drm_vop2.c | 13 ++++++++++++- >>> drivers/gpu/drm/rockchip/rockchip_drm_vop2.h | 4 ++++ >>> 2 files changed, 16 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c >>> index 498df0ce4680..87110beba366 100644 >>> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c >>> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop2.c >>> @@ -1554,6 +1554,7 @@ static void vop2_post_config(struct drm_crtc *crtc) >>> struct vop2_video_port *vp = to_vop2_video_port(crtc); >>> struct vop2 *vop2 = vp->vop2; >>> struct drm_display_mode *mode = &crtc->state->adjusted_mode; >>> + u64 bgcolor = crtc->state->background_color; >>> u16 vtotal = mode->crtc_vtotal; >>> u16 hdisplay = mode->crtc_hdisplay; >>> u16 hact_st = mode->crtc_htotal - mode->crtc_hsync_start; >>> @@ -1599,7 +1600,11 @@ static void vop2_post_config(struct drm_crtc *crtc) >>> vop2_vp_write(vp, RK3568_VP_POST_DSP_VACT_INFO_F1, val); >>> } >>> >>> - vop2_vp_write(vp, RK3568_VP_DSP_BG, 0); >>> + /* Background color is programmed with 10 bits of precision */ >>> + val = FIELD_PREP(RK3568_VP_DSP_BG__DSP_BG_RED, DRM_ARGB64_GETR_BPC(bgcolor, 10)); >>> + val |= FIELD_PREP(RK3568_VP_DSP_BG__DSP_BG_GREEN, DRM_ARGB64_GETG_BPC(bgcolor, 10)); >>> + val |= FIELD_PREP(RK3568_VP_DSP_BG__DSP_BG_BLUE, DRM_ARGB64_GETB_BPC(bgcolor, 10)); >> >> Division is expensive. If we convert a 16 bpc value to 10 bpc using >> direct bit-shifts, that is "DRM_ARGB64_GETX(bgcolor) >> 6" will >> keep the relative error within 1 compared to DIV_ROUND_CLOSEST(). >> >> Should we be concerned about the precision problem here? > > The precision was something I initially looked into for CRC verification, in the > context of the related IGT test. But since I've added the VKMS support, I think > we should not worry about that anymore. > > Moreover, as already pointed out in [1], only RK3576 supports CRC generation at > display controller level, and that is not particularly useful because it doesn't > take the background color into account. Therefore I had to capture the frame > CRCs at DisplayPort AUX channel level, by using the USB-C DP AltMode capable > port of my RK3588-based board. However, that solution is not yet available > upstream, as it requires further work for cleanup and improving the overall > USB-C reliability. > > Hence I'll move on with your suggestion and switch to the simple bit-shifting > approach for the next revision. Done in v4: https://lore.kernel.org/all/20251219-rk3588-bgcolor-v4-0-2ff1127ea757@collabora.com/