Andrzej Hajda <a.hajda@xxxxxxxxxxx> writes: > 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. It only changes the semantic if you past in a NULL host, from "oops" to "do something useful". > 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? > > I did not spent much time on this idea, so I cannot guarantee it has not > fundamental issues :) If component_add() isn't called during probe, then DSI would just get skipped during bind as far as I know. I *think* what you're thinking is moving DSI host register to probe, and then panel lookup stays in bind. That seems much more risky to me -- do we know for sure that no mipi_dsi_device will do any DSI transactions during its probe? I would expect some of them to.
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