linux-kernel - Re: [PATCH V8 08/12] drm/bridge: imx: add driver for HDMI TX Parallel Video Interface

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Date: Tue, 6 Feb 2024 11:52:59 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Adam Ford <aford173@...il.com>
Cc: linux-arm-kernel@...ts.infradead.org, marex@...x.de,
	alexander.stein@...tq-group.com, frieder.schrempf@...tron.de,
	Lucas Stach <l.stach@...gutronix.de>,
	Luca Ceresoli <luca.ceresoli@...tlin.com>,
	Richard Leitner <richard.leitner@...data.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Fabio Estevam <festevam@...il.com>,
	Andrzej Hajda <andrzej.hajda@...el.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Robert Foss <rfoss@...nel.org>, Jonas Karlman <jonas@...boo.se>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	NXP Linux Team <linux-imx@....com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Vinod Koul <vkoul@...nel.org>,
	Kishon Vijay Abraham I <kishon@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Liu Ying <victor.liu@....com>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-phy@...ts.infradead.org,
	linux-pm@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH V8 08/12] drm/bridge: imx: add driver for HDMI TX
 Parallel Video Interface

On Tue, Feb 06, 2024 at 12:50:16PM -0600, Adam Ford wrote:
> On Tue, Feb 6, 2024 at 11:06 AM Nathan Chancellor <nathan@...nel.org> wrote:
> >
> > Hi all,
> >
> > On Sat, Feb 03, 2024 at 10:52:48AM -0600, Adam Ford wrote:
> > > From: Lucas Stach <l.stach@...gutronix.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@...gutronix.de>
> > > Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com> (v7)
> > > Tested-by: Marek Vasut <marex@...x.de> (v1)
> > > Tested-by: Luca Ceresoli <luca.ceresoli@...tlin.com> (v7)
> > > Tested-by: Richard Leitner <richard.leitner@...data.com> (v2)
> > > Tested-by: Frieder Schrempf <frieder.schrempf@...tron.de> (v2)
> > > Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com> (v3)
> > > Reviewed-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> > > Tested-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> > > Tested-by: Fabio Estevam <festevam@...il.com>
> > > Signed-off-by: Adam Ford <aford173@...il.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.
> 
> I don't think we can turn the else-if into a blind else, because in
> order to make bus_flags point to bridge_state->input_bus_cfg.flags,
> bridge_state must not be NULL, but we could add an additional else to
> set bus_flags to 0, but I think the simplest thing to do would be to
> set bus_flags = 0 at the initialization on line 60 as it suggests.
> 
> If you agree, I can submit a patch later tonight.  I need to fix
> another issue found by the build-bot [1]  to make line 113 return NULL
> instead of 0 anyway.  I figured I could just fix them both at the same
> time.
> 
> [1] - https://lore.kernel.org/oe-kbuild-all/202402062134.a6CqAt3s-lkp@intel.com/

Seems reasonable to me, thanks!

Nathan