linux-kernel - Re: [PATCH v5 4/6] drm: Allow DSI devices to be registered before the host registers.

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Date:   Wed, 19 Jul 2017 13:31:47 -0700
From:   Eric Anholt <eric@...olt.net>
To:     dri-devel@...ts.freedesktop.org,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Thierry Reding <thierry.reding@...il.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/6] drm: Allow DSI devices to be registered before the host registers.

Eric Anholt <eric@...olt.net> writes:

> When a mipi_dsi_host is registered, the DT is walked to find any child
> nodes with compatible strings.  Those get registered as DSI devices,
> and most DSI panel drivers are mipi_dsi_drivers that attach to those nodes.
>
> There is one special case currently, the adv7533 bridge, where the
> bridge probes on I2C, and during the bridge attach step it looks up
> the mipi_dsi_host and registers the mipi_dsi_device (for its own stub
> mipi_dsi_driver).
>
> For the Raspberry Pi panel, though, we also need to attach on I2C (our
> control bus), but don't have a bridge driver.  The lack of a bridge's
> attach() step like adv7533 uses means that we aren't able to delay the
> mipi_dsi_device creation until the mipi_dsi_host is present.
>
> To fix this, we extend mipi_dsi_device_register_full() to allow being
> called with a NULL host, which puts the device on a queue waiting for
> a host to appear.  When a new host is registered, we fill in the host
> value and finish the device creation process.
>
> v2: Cleanly error out if one attempts to mipi_dsi_attach() without a
>     host.  Fix handling of DSI with multiple devices, and OF node
>     refcounting.
>
> Signed-off-by: Eric Anholt <eric@...olt.net>
> ---
>  drivers/gpu/drm/drm_mipi_dsi.c | 63 ++++++++++++++++++++++++++++++++++--------
>  include/drm/drm_mipi_dsi.h     |  3 ++
>  2 files changed, 54 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
> index 1160a579e0dc..77d439254da6 100644
> --- a/drivers/gpu/drm/drm_mipi_dsi.c
> +++ b/drivers/gpu/drm/drm_mipi_dsi.c

> @@ -295,6 +308,27 @@ int mipi_dsi_host_register(struct mipi_dsi_host *host)
>  
>  	mutex_lock(&host_lock);
>  	list_add_tail(&host->list, &host_list);
> +
> +	/* If any DSI devices were registered under our OF node, then
> +	 * connect our host to it and probe them now.
> +	 */
> +	list_for_each_entry_safe(dsi, temp, &unattached_device_list, list) {
> +		struct device_node *host_node = of_get_parent(dsi->dev.of_node);
> +
> +		if (!of_node_cmp(host_node->name, "ports"))
> +			host_node = of_get_next_parent(host_node);
> +
> +		if (host_node == host->dev->of_node) {
> +			dsi->host = host;
> +			dsi->dev.parent = host->dev;
> +			device_initialize(&dsi->dev);
> +
> +			mipi_dsi_device_add(dsi);
> +			list_del_init(&dsi->list);
> +		}
> +
> +		of_node_put(host_node);
> +	}

Kbuild test caught that of_get_next_parent() isn't defined for
!CONFIG_OF, so I've put this loop under IS_ENABLED(CONFIG_OF) for v3.

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