linux-kernel - Re: [PATCH 6/8] drm: Allow DSI devices to be registered before the host registers.

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Date:   Fri, 14 Jul 2017 15:58:43 -0700
From:   Eric Anholt <eric@...olt.net>
To:     Archit Taneja <architt@...eaurora.org>,
        dri-devel@...ts.freedesktop.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,
        Boris Brezillon <boris.brezillon@...e-electrons.com>
Subject: Re: [PATCH 6/8] drm: Allow DSI devices to be registered before the host registers.

Archit Taneja <architt@...eaurora.org> writes:

> On 06/28/2017 01:28 AM, Eric Anholt wrote:
>> 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.
>
> This is quite a nice idea. The only bothering thing is the info.of_node usage
> varies between child nodes (mipi_dsi_devs) and non-child nodes (i2c control
> bus).
>
> For DSI children expressed in DT, the of_node in info holds the DT node
> corresponding to the DSI child itself. For non-DT ones, this patch assumes
> that info.of_node stores the DSI host DT node. I think it should be okay as
> long as we mention the usage in a comment somewhere. The other option is to
> have a new info.host_node field to keep a track of the host DT node.

I think maybe you misread the patch?  We're using
of_get_parent(dsi->dev.node), which came from info->node, to compare to
host->dev->of_node().

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