Archit Taneja <architt@xxxxxxxxxxxxxx> writes: > On 06/29/2017 04:09 PM, Andrzej Hajda wrote: >> On 29.06.2017 07:03, Archit Taneja wrote: >>> >>> 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. >> >> Field abuse is not a biggest issue. >> >> This patch changes totally semantic of mipi_dsi_device_register_full. >> Currently semantic of *_device_register* function is to create and add >> device to existing bus, ie after return we have device attached to bus, >> so it can be instantly used. With this change function can return some >> unattached device, without warranty it will be ever attached - kind of >> hidden deferring. Such change looks for me quite dangerous, even if it >> looks convenient in this case. >> >> As discussed in other thread more appealing solution for me would be: >> 1. host creates dsi bus, but doesn't call component_add as it does not >> have all required resources. >> 2. host waits for all required dsi devs attached, gets registered panels >> or bridges and calls component_add after that. >> 3. in bind phase it has all it needs, hasn't it? > > This seems like it would work, but would require KMS drivers to restructure > themselves around this approach. For KMS drivers that don't even use the > component stuff, it might be asking too much. > > We could maybe consider Eric's patch as an intermediate solution, we should > definitely put WARN_ON(!dsi->host) like checks for all the existing > mipi_dsi_*() API. Could you clarify which entrypoints you'd like a warning on? Is it just "everything that gets the host ops"?
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