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

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Message-ID: <aNFkn0zXFJQE0r5C@lizhi-Precision-Tower-5810>
Date: Mon, 22 Sep 2025 11:00:47 -0400
From: Frank Li <Frank.li@....com>
To: Liu Ying <victor.liu@....com>
Cc: Philipp Zabel <p.zabel@...gutronix.de>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Dmitry Baryshkov <lumag@...nel.org>,
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/14] drm/imx: dc: Use TCON operation mode

On Mon, Sep 22, 2025 at 11:48:26AM +0800, Liu Ying wrote:
> On 09/19/2025, Frank Li wrote:
> > On Fri, Jul 04, 2025 at 05:03:55PM +0800, Liu Ying wrote:
> >> 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@....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(-)
> >>
> > ...
> >> @@ -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?

Okay! That should be fine.

Frank

>
> >
> >>
> >>  	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);
> >>
> > ...
> >
> >>
> >> --
> >> 2.34.1
> >>
>
>
> --
> Regards,
> Liu Ying