linux-kernel - Re: [PATCH 1/8] drm: bridge: Add support for static image formats

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Date:   Thu, 26 Apr 2018 22:57:11 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     jacopo mondi <jacopo@...ndi.org>
Cc:     Jacopo Mondi <jacopo+renesas@...ndi.org>, architt@...eaurora.org,
        a.hajda@...sung.com, airlied@...ux.ie, daniel@...ll.ch,
        peda@...ntia.se, linux-renesas-soc@...r.kernel.org,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] drm: bridge: Add support for static image formats

Hi Jacopo,

On Thursday, 26 April 2018 21:40:56 EEST jacopo mondi wrote:
> On Mon, Apr 23, 2018 at 12:27:39PM +0300, Laurent Pinchart wrote:
> > On Thursday, 19 April 2018 12:31:02 EEST Jacopo Mondi wrote:
> >> Add support for storing image format information in DRM bridges with
> >> associated helper function.
> >> 
> >> This patch replicates for bridges what
> >> 'drm_display_info_set_bus_formats()'
> >> is for connectors.
> >> 
> >> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> >> ---
> >>  drivers/gpu/drm/drm_bridge.c | 30 ++++++++++++++++++++++++++++++
> >>  include/drm/drm_bridge.h     |  8 ++++++++
> >>  2 files changed, 38 insertions(+)
> >> 
> >> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> >> index 1638bfe..e2ad098 100644
> >> --- a/drivers/gpu/drm/drm_bridge.c
> >> +++ b/drivers/gpu/drm/drm_bridge.c
> >> @@ -157,6 +157,36 @@ void drm_bridge_detach(struct drm_bridge *bridge)
> >>  }
> >>  
> >>  /**
> >> + * drm_bridge_set_bus_formats() - set bridge supported image formats
> >> + * @bridge: the bridge to set image formats in
> >> + * @formats: array of MEDIA_BUS_FMT\_ supported image formats
> > 
> > Why the \ (here and below) ?
> 
> mmm, I can't tell where I made that up from... Will change with
> MEDIA_BUS_FMT_*
> 
> >> + * @num_formats: number of elements in the @formats array
> >> + *
> >> + * Store a list of supported image formats in a bridge.
> >> + * See MEDIA_BUS_FMT_* definitions in
> >> include/uapi/linux/media-bus-format.h for
> >> + * a full list of available formats.
> >> + */
> >> +int drm_bridge_set_bus_formats(struct drm_bridge *bridge, const u32
> >> *formats,
> >> +			       unsigned int num_formats)
> >> +{
> >> +	u32 *fmts;
> >> +
> >> +	if (!formats || !num_formats)
> >> +		return -EINVAL;
> >> +
> >> +	fmts = kmemdup(formats, sizeof(*formats) * num_formats, GFP_KERNEL);
> > 
> > This memory will be leaked when the bridge is destroyed.
> 
> Right. I'm afraid this may open a pandora box, but, ehm, where is the
> bridge objects lifetime managed? The best I can think of is to use the
> resource managed version of kmemdup, associating that memory to
> the drm_device device object. That means the memory will be freed at
> DRM pipeline teardown time only if I'm not wrong. Can a bridge be
> destroyed before that?

The lifetime of the bridge is independent from the lifetime of the drm_device, 
so that won't work. It looks like we need to add a bridge cleanup operation 
:-/ You're right, it opens pandora's box.

My recommendation is to add a .release() operation to the bridge ops 
structure, and to implement a drm_bridge_cleanup() function that frees the 
bus_formats memory. Then, a drm_bridge_release() function can wrap the 
release() ops, and that should be called from the bridge driver .remove() 
handler. Or even butter, call the drm_bridge_release() function 
drm_bridge_put(), to pave the way for a reference-count-based implementation.

> >> +	if (!fmts)
> >> +		return -ENOMEM;
> >> +
> >> +	kfree(bridge->bus_formats);
> >> +	bridge->bus_formats = fmts;
> >> +	bridge->num_bus_formats = num_formats;
> >> +
> >> +	return 0;
> >> +}
> >> +EXPORT_SYMBOL(drm_bridge_set_bus_formats);
> >> +
> >> +/**
> >>   * DOC: bridge callbacks
> >>   *
> >>   * The &drm_bridge_funcs ops are populated by the bridge driver. The
> >>   DRM
> >> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> >> index 3270fec..6b3648c 100644
> >> --- a/include/drm/drm_bridge.h
> >> +++ b/include/drm/drm_bridge.h
> >> @@ -258,6 +258,9 @@ struct drm_bridge_timings {
> >>   * @encoder: encoder to which this bridge is connected
> >>   * @next: the next bridge in the encoder chain
> >>   * @of_node: device node pointer to the bridge
> >> + * @bus_formats: wire image formats. Array of @num_bus_formats
> >> MEDIA_BUS_FMT\_
> >> + * elements
> >> + * @num_bus_formats: size of @bus_formats array
> >>   * @list: to keep track of all added bridges
> >>   * @timings: the timing specification for the bridge, if any (may
> >>   * be NULL)
> >> @@ -271,6 +274,9 @@ struct drm_bridge {
> >>  #ifdef CONFIG_OF
> >>  	struct device_node *of_node;
> >>  #endif
> >> +	const u32 *bus_formats;
> >> +	unsigned int num_bus_formats;
> >> +
> >>  	struct list_head list;
> >>  	const struct drm_bridge_timings *timings;
> >> 
> >> @@ -296,6 +302,8 @@ void drm_bridge_mode_set(struct drm_bridge *bridge,
> >>  			struct drm_display_mode *adjusted_mode);
> >>  void drm_bridge_pre_enable(struct drm_bridge *bridge);
> >>  void drm_bridge_enable(struct drm_bridge *bridge);
> >> +int drm_bridge_set_bus_formats(struct drm_bridge *bridge, const u32
> >> *fmts,
> >> +			       unsigned int num_fmts);
> >> 
> >>  #ifdef CONFIG_DRM_PANEL_BRIDGE
> >>  struct drm_bridge *drm_panel_bridge_add(struct drm_panel *panel,

-- 
Regards,

Laurent Pinchart