[PATCH] drm/stm: Fix bus_flags handling

[Sam Ravnborg]

Hi Marek.

On Sat, Oct 03, 2020 at 01:07:26AM +0200, Marek Vasut wrote:
> The drm_display_mode_to_videomode() does not populate DISPLAY_FLAGS_DE_LOW
> or DISPLAY_FLAGS_PIXDATA_NEGEDGE flags in struct videomode.

So after reading this paragrahp I assumed this patch would fix this, alas
there is no changes to drm_modes.c.
Rather than introducing hacks could we try to fix the root cause here?

Root cause - as you point out is that there is missing some flags in
the conversion.
Another point is that the stm driver could drop the use of
drm_display_mode_to_videomode() - all the information is available in drm_display_mode
and using drm_display_mode_to_videomode() does not help much.

If the point is to have easier access to hsync and friendns maybe we
should have a few helpers operating direct on display_mode and not this
conversion to video_mode which is something that belongs to fbdev and
should IMO not be used inside a drm driver.

	Sam

> Therefore, no
> matter what polarity the next bridge or display might require, these flags
> are never set, and thus the LTDC GCR_DEPOL and GCR_PCPOL bits are never set,
> and the LTDC behaves as if both DISPLAY_FLAGS_PIXDATA_POSEDGE and
> DISPLAY_FLAGS_DE_HIGH were always set.
> 
> The fix for this problem is taken almost verbatim from MXSFB driver. In
> case there is a bridge attached to the LTDC, the bridge might have extra
> polarity requirements, so extract bus_flags from the bridge and use them
> for LTDC configuration. Otherwise, extract bus_flags from the connector,
> which is the display.
> 
> Fixes: b759012c5fa7 ("drm/stm: Add STM32 LTDC driver")
> Signed-off-by: Marek Vasut <marex at denx.de>
> Cc: Alexandre Torgue <alexandre.torgue at st.com>
> Cc: Antonio Borneo <antonio.borneo at st.com>
> Cc: Benjamin Gaignard <benjamin.gaignard at st.com>
> Cc: Maxime Coquelin <mcoquelin.stm32 at gmail.com>
> Cc: Philippe Cornu <philippe.cornu at st.com>
> Cc: Sam Ravnborg <sam at ravnborg.org>
> Cc: Vincent Abriou <vincent.abriou at st.com>
> Cc: Yannick Fertre <yannick.fertre at st.com>
> Cc: linux-arm-kernel at lists.infradead.org
> Cc: linux-stm32 at st-md-mailman.stormreply.com
> To: dri-devel at lists.freedesktop.org
> ---
>  drivers/gpu/drm/stm/ltdc.c | 22 ++++++++++++++++++++--
>  drivers/gpu/drm/stm/ltdc.h |  2 ++
>  2 files changed, 22 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
> index 07c73079293c..a282a1553497 100644
> --- a/drivers/gpu/drm/stm/ltdc.c
> +++ b/drivers/gpu/drm/stm/ltdc.c
> @@ -546,11 +546,17 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
>  	struct drm_device *ddev = crtc->dev;
>  	struct drm_display_mode *mode = &crtc->state->adjusted_mode;
>  	struct videomode vm;
> +	u32 bus_flags = 0;
>  	u32 hsync, vsync, accum_hbp, accum_vbp, accum_act_w, accum_act_h;
>  	u32 total_width, total_height;
>  	u32 val;
>  	int ret;
>  
> +	if (ldev->bridge)
> +		bus_flags = ldev->bridge->timings->input_bus_flags;
> +	else if (ldev->connector)
> +		bus_flags = ldev->connector->display_info.bus_flags;
> +
>  	if (!pm_runtime_active(ddev->dev)) {
>  		ret = pm_runtime_get_sync(ddev->dev);
>  		if (ret) {
> @@ -586,10 +592,10 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
>  	if (vm.flags & DISPLAY_FLAGS_VSYNC_HIGH)
>  		val |= GCR_VSPOL;
>  
> -	if (vm.flags & DISPLAY_FLAGS_DE_LOW)
> +	if (bus_flags & DRM_BUS_FLAG_DE_LOW)
>  		val |= GCR_DEPOL;
>  
> -	if (vm.flags & DISPLAY_FLAGS_PIXDATA_NEGEDGE)
> +	if (bus_flags & DRM_BUS_FLAG_PIXDATA_DRIVE_NEGEDGE)
>  		val |= GCR_PCPOL;
>  
>  	reg_update_bits(ldev->regs, LTDC_GCR,
> @@ -1098,6 +1104,8 @@ static const struct drm_encoder_helper_funcs ltdc_encoder_helper_funcs = {
>  
>  static int ltdc_encoder_init(struct drm_device *ddev, struct drm_bridge *bridge)
>  {
> +	struct ltdc_device *ldev = ddev->dev_private;
> +	struct drm_connector_list_iter iter;
>  	struct drm_encoder *encoder;
>  	int ret;
>  
> @@ -1119,6 +1127,16 @@ static int ltdc_encoder_init(struct drm_device *ddev, struct drm_bridge *bridge)
>  		return -EINVAL;
>  	}
>  
> +	ldev->bridge = bridge;
> +
> +	/*
> +	 * Get hold of the connector. This is a bit of a hack, until the bridge
> +	 * API gives us bus flags and formats.
> +	 */
> +	drm_connector_list_iter_begin(ddev, &iter);
> +	ldev->connector = drm_connector_list_iter_next(&iter);
> +	drm_connector_list_iter_end(&iter);
> +
>  	DRM_DEBUG_DRIVER("Bridge encoder:%d created\n", encoder->base.id);
>  
>  	return 0;
> diff --git a/drivers/gpu/drm/stm/ltdc.h b/drivers/gpu/drm/stm/ltdc.h
> index f153b908c70e..d0d2c81de29a 100644
> --- a/drivers/gpu/drm/stm/ltdc.h
> +++ b/drivers/gpu/drm/stm/ltdc.h
> @@ -38,6 +38,8 @@ struct ltdc_device {
>  	u32 irq_status;
>  	struct fps_info plane_fpsi[LTDC_MAX_LAYER];
>  	struct drm_atomic_state *suspend_state;
> +	struct drm_bridge *bridge;
> +	struct drm_connector *connector;
>  };
>  
>  int ltdc_load(struct drm_device *ddev);
> -- 
> 2.28.0
> 
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