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

[Archit Taneja <architt@codeaurora.org>]

On 07/19/2017 01:43 AM, Eric Anholt wrote:
> Archit Taneja <architt@codeaurora.org> writes:
> 
>> On 07/15/2017 04:28 AM, Eric Anholt wrote:
>>> Archit Taneja <architt@codeaurora.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().
>>
>> I think I did misread it.
>>
>> Although, I'm not entirely clear what we should be setting info.node to.
>> In patch #8, info.node is set by:
>>
>> 	endpoint = of_graph_get_next_endpoint(dev->of_node, NULL);
>> 	info.node = of_graph_get_remote_port(endpoint);
>>
>> Looking at the dt bindings in patch #7, it looks like info.node is set
>> to the 'port' device node in dsi@7e700000, is that right?
> 
> Yeah.
> 
> 
>> I suppose 'port' here seems like a reasonable representation of
>> dsi->dev.node, I wonder how it would work if the dsi host had multiple
>> ports underneath it. I.e:
>>
>> dsi@7e700000 {
>> 	...
>> 	...
>> 	ports {
>> 		port@0 {
>> 			...
>> 			dsi_out_port: endpoint {
>> 				remote-endpoint = <&panel_dsi_port>;
>> 			};
>> 		};
>> 		port@1 {
>> 			...
>> 			...
>> 		};
>> 	};
>> };
>>
>> Here, we would need to set info.node to the 'ports' node, so that
>> of_get_parent(dsi->dev.of_node) equals host->dev->of_node. That doesn't
>> seem correct.
>>
>> Ideally, a dev's 'of_node' should be left to NULL if we don't have a
>> corresponding OF node. We're sort of overriding it here since we don't
>> have any other place to store this information in the mipi_dsi_device
>> struct.
>>
>> Maybe we could add a 'host_node' entry in mipi_dsi_device itself, which
>> is exclusively used cases where the DSI device doesn't have a DT node.
>> Our check in mipi_dsi_host_register() could then be something like:
> 
> I think instead of extending the struct, we can just walk to the parent
> similarly to how of_graph_get_remove_port_parent() does.  And fix some
> node refcounting at the same time:

Yeah, I guess this works. The only thing that's a slight irritant is that
we're setting an 'of_node' to a device that doesn't have a DT
representation. But I don't have any strong feelings against it.

Reviewed-by: Archit Taneja <architt@codeaurora.org>

> 
> diff --git a/drivers/gpu/drm/drm_mipi_dsi.c b/drivers/gpu/drm/drm_mipi_dsi.c
> index ed3d505dc203..77d439254da6 100644
> --- a/drivers/gpu/drm/drm_mipi_dsi.c
> +++ b/drivers/gpu/drm/drm_mipi_dsi.c
> @@ -313,7 +313,12 @@ int mipi_dsi_host_register(struct mipi_dsi_host *host)
>           * connect our host to it and probe them now.
>           */
>          list_for_each_entry_safe(dsi, temp, &unattached_device_list, list) {
> -               if (of_get_parent(dsi->dev.of_node) == host->dev->of_node) {
> +               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);
> @@ -321,6 +326,8 @@ int mipi_dsi_host_register(struct mipi_dsi_host *host)
>                          mipi_dsi_device_add(dsi);
>                          list_del_init(&dsi->list);
>                  }
> +
> +               of_node_put(host_node);
>          }
>          mutex_unlock(&host_lock);
>   
> 

-- 
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