Re: [PATCH V4] drm/stm: Fix bus_flags handling

[yannick Fertre <yannick.fertre@foss.st.com>]

Hi Marek,
Thanks for the patch.

Tested-by: Yannick Fertre <yannick.fertre@foss.st.com>



On 1/27/21 12:07 PM, 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. 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@denx.de>
> Signed-off-by: Yannick Fertre <yannick.fertre@st.com>
> Cc: Alexandre Torgue <alexandre.torgue@st.com>
> Cc: Antonio Borneo <antonio.borneo@st.com>
> Cc: Benjamin Gaignard <benjamin.gaignard@st.com>
> Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
> Cc: Philippe Cornu <philippe.cornu@st.com>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: Vincent Abriou <vincent.abriou@st.com>
> Cc: Yannick Fertre <yannick.fertre@st.com>
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-stm32@st-md-mailman.stormreply.com
> To: dri-devel@lists.freedesktop.org
> ---
> V2: Check if ldev->bridge->timings is non-NULL before accessing it
> V3: get bus_flags from connector (from Yannick)
>      - Display controller could support several connectors (not connected at
>        the same time). ie: stm32mp15c-DK2 board have 2 connectors (HDMI + DSI).
>        Driver check which connector is connected to get the bus flag.
> V4: get bridge from encoder (from Yannick)
> ---
>   drivers/gpu/drm/stm/ltdc.c | 33 +++++++++++++++++++++++++++++++--
>   1 file changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
> index 6e28e6b60e72..acc9f6694eb6 100644
> --- a/drivers/gpu/drm/stm/ltdc.c
> +++ b/drivers/gpu/drm/stm/ltdc.c
> @@ -544,13 +544,42 @@ static void ltdc_crtc_mode_set_nofb(struct drm_crtc *crtc)
>   {
>   	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
>   	struct drm_device *ddev = crtc->dev;
> +	struct drm_connector_list_iter iter;
> +	struct drm_connector *connector = NULL;
> +	struct drm_encoder *encoder = NULL;
> +	struct drm_bridge *bridge = NULL;
>   	struct drm_display_mode *mode = &crtc->state->adjusted_mode;
>   	struct videomode vm;
>   	u32 hsync, vsync, accum_hbp, accum_vbp, accum_act_w, accum_act_h;
>   	u32 total_width, total_height;
> +	u32 bus_flags = 0;
>   	u32 val;
>   	int ret;
>   
> +	/* get encoder from crtc */
> +	drm_for_each_encoder(encoder, ddev)
> +		if (encoder->crtc == crtc)
> +			break;
> +
> +	if (encoder) {
> +		/* get bridge from encoder */
> +		list_for_each_entry(bridge, &encoder->bridge_chain, chain_node)
> +			if (bridge->encoder == encoder)
> +				break;
> +
> +		/* Get the connector from encoder */
> +		drm_connector_list_iter_begin(ddev, &iter);
> +		drm_for_each_connector_iter(connector, &iter)
> +			if (connector->encoder == encoder)
> +				break;
> +		drm_connector_list_iter_end(&iter);
> +	}
> +
> +	if (bridge && bridge->timings)
> +		bus_flags = bridge->timings->input_bus_flags;
> +	else if (connector)
> +		bus_flags = connector->display_info.bus_flags;
> +
>   	if (!pm_runtime_active(ddev->dev)) {
>   		ret = pm_runtime_get_sync(ddev->dev);
>   		if (ret) {
> @@ -586,10 +615,10 @@ 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,
> 

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