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    SubjectRe: [PATCH 6/8] drm: Allow DSI devices to be registered before the host registers.
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    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);
    >
    >

    --
    Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
    a Linux Foundation Collaborative Project

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