Re: [PATCH 08/14] drm/imx: dc: Use TCON operation mode

On 09/19/2025, Frank Li wrote:

On Fri, Jul 04, 2025 at 05:03:55PM +0800, Liu Ying wrote:

quoted

In TCON operation mode, sync signals from FrameGen are ignored, but
a much more customized output timing can be generated by the TCON
module.  By using TCON operaton mode, generate KACHUNK signal along
with HSYNC/VSYNC/data enable signals.  The KACHUNK signal is used as
a synchronization signal inside the prefetch engine(DPRC + PRG(s),
attached to FetchUnit(s)).  Carefully switch TCON bypass mode to TCON
operation mode when CRTC is being enabled so that the prefetch engine
may evade the first dumb frame generated by the display controller.

Since TCON BYPASS bit is controlled by KMS driver when doing atomic
commits, drop the bit setting when initializing TCON.  This also
avoids accidentally initializing TCON BYPASS bit to 1 when driver
module removing and re-installing where an upcoming patch would
disable a CRTC at boot in TCON operation mode if needed.

Signed-off-by: Liu Ying <victor.liu@nxp.com>
---
 drivers/gpu/drm/imx/dc/dc-crtc.c |  28 ++++++++++
 drivers/gpu/drm/imx/dc/dc-de.h   |   2 +
 drivers/gpu/drm/imx/dc/dc-kms.h  |   2 +
 drivers/gpu/drm/imx/dc/dc-tc.c   | 114 +++++++++++++++++++++++++++++++++++++--
 4 files changed, 142 insertions(+), 4 deletions(-)

...

quoted

@@ -249,6 +260,7 @@ dc_crtc_atomic_enable(struct drm_crtc *crtc, struct drm_atomic_state *state)
 	enable_irq(dc_crtc->irq_ed_safe_shdload);

 	dc_fg_cfg_videomode(dc_crtc->fg, adj);
+	dc_tc_cfg_videomode(dc_crtc->tc, adj);

 	dc_cf_framedimensions(dc_crtc->cf_cont,
 			      adj->crtc_hdisplay, adj->crtc_vdisplay);

@@ -273,7 +285,22 @@ dc_crtc_atomic_enable(struct drm_crtc *crtc, struct drm_atomic_state *state)
 	dc_ed_pec_sync_trigger(dc_crtc->ed_cont);
 	dc_ed_pec_sync_trigger(dc_crtc->ed_safe);
 	dc_fg_shdtokgen(dc_crtc->fg);
+
+	/* Don't relinquish CPU until TCON is set to operation mode. */
+	local_irq_save(flags);
+	preempt_disable();
+
 	dc_fg_enable(dc_crtc->fg);
+	/*
+	 * Turn TCON into operation mode as soon as the first dumb
+	 * frame is generated by DC(we don't relinquish CPU to ensure
+	 * this).  This makes DPR/PRG be able to evade the frame.
+	 */
+	DC_CRTC_WAIT_FOR_FRAMEGEN_FRAME_INDEX_MOVING(dc_crtc->fg);
+	dc_tc_set_operation_mode(dc_crtc->tc);
+
+	local_irq_restore(flags);
+	preempt_enable();

Does it need reverised order?

I'm referring to __raw_spin_lock_irqsave() and __raw_spin_unlock_irqrestore()
to do this right, where local IRQ is saved/restored prior to preemption
disablement/enablement.  Am I missing anything?

quoted

 	DC_CRTC_WAIT_FOR_COMPLETION_TIMEOUT(ed_safe_shdload_done);
 	DC_CRTC_WAIT_FOR_COMPLETION_TIMEOUT(ed_cont_shdload_done);

@@ -561,6 +588,7 @@ int dc_crtc_init(struct dc_drm_device *dc_drm, int crtc_index)
 	dc_crtc->ed_cont = pe->ed_cont[crtc_index];
 	dc_crtc->ed_safe = pe->ed_safe[crtc_index];
 	dc_crtc->fg = de->fg;
+	dc_crtc->tc = de->tc;

 	dc_crtc->irq_dec_framecomplete = de->irq_framecomplete;
 	dc_crtc->irq_dec_seqcomplete = de->irq_seqcomplete;

diff --git a/drivers/gpu/drm/imx/dc/dc-de.h b/drivers/gpu/drm/imx/dc/dc-de.h
index 211f3fcc1a9ad642617d3b22e35ea923f75e645b..c39f2ef5eea98c3eb6ae9b5392f9bf9f7e33e7c5 100644
--- a/drivers/gpu/drm/imx/dc/dc-de.h
+++ b/drivers/gpu/drm/imx/dc/dc-de.h

@@ -54,6 +54,8 @@ enum drm_mode_status dc_fg_check_clock(struct dc_fg *fg, int clk_khz);
 void dc_fg_init(struct dc_fg *fg);

...

quoted

--
2.34.1

-- 
Regards,
Liu Ying