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([183.91.15.56]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ccc9bdb9bbsm8569795ad.4.2026.07.07.02.30.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Jul 2026 02:30:28 -0700 (PDT) From: phucduc.bui@gmail.com To: Laurent Pinchart , Geert Uytterhoeven , Maarten Lankhorst Cc: Maxime Ripard , Thomas Zimmermann , Simona Vetter , dri-devel@lists.freedesktop.org, linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org, bui duc phuc Subject: [PATCH v4] drm: shmobile: Fix white screen after resume when LCDC is stopped Date: Tue, 7 Jul 2026 16:30:04 +0700 Message-ID: <20260707093004.987846-1-phucduc.bui@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: bui duc phuc The LCDC on R8A7740 may show a completely white screen after resuming from suspend (s2idle or s2ram). After resume, both Set A and Set B registers are reset to 0. As the Frame End interrupt is not generated while the controller is stopped (DO=0), the hardware register switching mechanism is not triggered. Consequently, Set A remains at 0x00000000 even though a valid Start Address is written to Set B, resulting in a white screen. This is a timing-dependent race condition. In some configurations, debug options slow down the resume path enough for a Frame End interrupt to occur, which can mask the issue. Fix this by priming both register sets with the Start Address while the controller is stopped, ensuring a valid base address is available immediately after resume. Tested-by: Geert Uytterhoeven Reviewed-by: Geert Uytterhoeven Signed-off-by: bui duc phuc --- Note: It was originally posted in March and has already received both Reviewed-by and Tested-by tags. I'm resending it to bring it back to attention in case it was overlooked. Changes in v4: - No functional changes. - Resend. Changes: - v3 Update commit message, add Tested-by and Reviewed-by tags - v2 Fix incorrect use of lcdc_write_mirror() for LDSA2R in the DO=0 path; use lcdc_write() to update both register sets as intended. .../gpu/drm/renesas/shmobile/shmob_drm_plane.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/renesas/shmobile/shmob_drm_plane.c b/drivers/gpu/drm/renesas/shmobile/shmob_drm_plane.c index 148de34af785..92e7fb464cb3 100644 --- a/drivers/gpu/drm/renesas/shmobile/shmob_drm_plane.c +++ b/drivers/gpu/drm/renesas/shmobile/shmob_drm_plane.c @@ -70,6 +70,7 @@ static void shmob_drm_primary_plane_setup(struct shmob_drm_plane *splane, struct shmob_drm_plane_state *sstate = to_shmob_plane_state(state); struct shmob_drm_device *sdev = to_shmob_device(splane->base.dev); struct drm_framebuffer *fb = state->fb; + u32 ldcnt2r; /* TODO: Handle YUV colorspaces. Hardcode REC709 for now. */ lcdc_write(sdev, LDDFR, sstate->format->lddfr | LDDFR_CF1); @@ -78,11 +79,19 @@ static void shmob_drm_primary_plane_setup(struct shmob_drm_plane *splane, /* Word and long word swap. */ lcdc_write(sdev, LDDDSR, sstate->format->ldddsr); - lcdc_write_mirror(sdev, LDSA1R, sstate->dma[0]); - if (shmob_drm_format_is_yuv(sstate->format)) - lcdc_write_mirror(sdev, LDSA2R, sstate->dma[1]); + ldcnt2r = lcdc_read(sdev, LDCNT2R); + + if (ldcnt2r & LDCNT2R_DO) { + lcdc_write_mirror(sdev, LDSA1R, sstate->dma[0]); + if (shmob_drm_format_is_yuv(sstate->format)) + lcdc_write_mirror(sdev, LDSA2R, sstate->dma[1]); - lcdc_write(sdev, LDRCNTR, lcdc_read(sdev, LDRCNTR) ^ LDRCNTR_MRS); + lcdc_write(sdev, LDRCNTR, lcdc_read(sdev, LDRCNTR) ^ LDRCNTR_MRS); + } else { + lcdc_write(sdev, LDSA1R, sstate->dma[0]); + if (shmob_drm_format_is_yuv(sstate->format)) + lcdc_write(sdev, LDSA2R, sstate->dma[1]); + } } static void shmob_drm_overlay_plane_setup(struct shmob_drm_plane *splane, -- 2.43.0