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Date: Tue, 6 Feb 2024 10:06:32 -0700
From: Nathan Chancellor <nathan@kernel.org>
To: Adam Ford <aford173@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org, marex@denx.de,
	alexander.stein@ew.tq-group.com, frieder.schrempf@kontron.de,
	Lucas Stach <l.stach@pengutronix.de>,
	Luca Ceresoli <luca.ceresoli@bootlin.com>,
	Richard Leitner <richard.leitner@skidata.com>,
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Subject: Re: [PATCH V8 08/12] drm/bridge: imx: add driver for HDMI TX
 Parallel Video Interface
Message-ID: <20240206170632.GA2183819@dev-arch.thelio-3990X>
References: <20240203165307.7806-1-aford173@gmail.com>
 <20240203165307.7806-9-aford173@gmail.com>
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In-Reply-To: <20240203165307.7806-9-aford173@gmail.com>

Hi all,

On Sat, Feb 03, 2024 at 10:52:48AM -0600, Adam Ford wrote:
> From: Lucas Stach <l.stach@pengutronix.de>
> 
> This IP block is found in the HDMI subsystem of the i.MX8MP SoC. It has a
> full timing generator and can switch between different video sources. On
> the i.MX8MP however the only supported source is the LCDIF. The block
> just needs to be powered up and told about the polarity of the video
> sync signals to act in bypass mode.
> 
> Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com> (v7)
> Tested-by: Marek Vasut <marex@denx.de> (v1)
> Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com> (v7)
> Tested-by: Richard Leitner <richard.leitner@skidata.com> (v2)
> Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de> (v2)
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> (v3)
> Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
> Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
> Tested-by: Fabio Estevam <festevam@gmail.com>
> Signed-off-by: Adam Ford <aford173@gmail.com>

<snip>

> diff --git a/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-pvi.c b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-pvi.c
> new file mode 100644
> index 000000000000..a76b7669fe8a
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-pvi.c
..
> +static void imx8mp_hdmi_pvi_bridge_enable(struct drm_bridge *bridge,
> +					  struct drm_bridge_state *bridge_state)
> +{
> +	struct drm_atomic_state *state = bridge_state->base.state;
> +	struct imx8mp_hdmi_pvi *pvi = to_imx8mp_hdmi_pvi(bridge);
> +	struct drm_connector_state *conn_state;
> +	const struct drm_display_mode *mode;
> +	struct drm_crtc_state *crtc_state;
> +	struct drm_connector *connector;
> +	u32 bus_flags, val;
> +
> +	connector = drm_atomic_get_new_connector_for_encoder(state, bridge->encoder);
> +	conn_state = drm_atomic_get_new_connector_state(state, connector);
> +	crtc_state = drm_atomic_get_new_crtc_state(state, conn_state->crtc);
> +
> +	if (WARN_ON(pm_runtime_resume_and_get(pvi->dev)))
> +		return;
> +
> +	mode = &crtc_state->adjusted_mode;
> +
> +	val = FIELD_PREP(PVI_CTRL_MODE_MASK, PVI_CTRL_MODE_LCDIF) | PVI_CTRL_EN;
> +
> +	if (mode->flags & DRM_MODE_FLAG_PVSYNC)
> +		val |= PVI_CTRL_OP_VSYNC_POL | PVI_CTRL_INP_VSYNC_POL;
> +
> +	if (mode->flags & DRM_MODE_FLAG_PHSYNC)
> +		val |= PVI_CTRL_OP_HSYNC_POL | PVI_CTRL_INP_HSYNC_POL;
> +
> +	if (pvi->next_bridge->timings)
> +		bus_flags = pvi->next_bridge->timings->input_bus_flags;
> +	else if (bridge_state)
> +		bus_flags = bridge_state->input_bus_cfg.flags;
> +
> +	if (bus_flags & DRM_BUS_FLAG_DE_HIGH)
> +		val |= PVI_CTRL_OP_DE_POL | PVI_CTRL_INP_DE_POL;
> +
> +	writel(val, pvi->regs + HTX_PVI_CTRL);
> +}

Apologies if this has already been reported or fixed, I searched lore
and did not find anything. Clang warns (or errors with CONFIG_WERROR=y)
for this function:

  drivers/gpu/drm/bridge/imx/imx8mp-hdmi-pvi.c:81:11: error: variable 'bus_flags' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
     81 |         else if (bridge_state)
        |                  ^~~~~~~~~~~~
  drivers/gpu/drm/bridge/imx/imx8mp-hdmi-pvi.c:84:6: note: uninitialized use occurs here
     84 |         if (bus_flags & DRM_BUS_FLAG_DE_HIGH)
        |             ^~~~~~~~~
  drivers/gpu/drm/bridge/imx/imx8mp-hdmi-pvi.c:81:7: note: remove the 'if' if its condition is always true
     81 |         else if (bridge_state)
        |              ^~~~~~~~~~~~~~~~~
     82 |                 bus_flags = bridge_state->input_bus_cfg.flags;
  drivers/gpu/drm/bridge/imx/imx8mp-hdmi-pvi.c:60:15: note: initialize the variable 'bus_flags' to silence this warning
     60 |         u32 bus_flags, val;
        |                      ^
        |                       = 0
  1 error generated.

This seems legitimate. If bridge_state can be NULL, should bus_flags be
initialized to zero like it suggests or should that 'else if' be turned
into a plain 'else'? I am happy to send a patch with that guidance.

Cheers,
Nathan