Hi Sudeep,
On Thu, 19 Jan 2023 at 09:46, Sudeep Holla sudeep.holla@arm.com wrote:
Hi Abdellatif,
On Thu, Jan 19, 2023 at 04:31:57PM +0000, Abdellatif El Khlifi wrote:
Hi Simon, Tom,
The FF-A transport is a SW bus and is not associated to any HW peripheral or undiscoverable base address.
There is only 1 way of discovering the FF-A bus and it's through the FF-A SW interfaces. The FF-A spec [1] describes this in details.
Discovering means gathering information about the FF-A framework such as: the FF-A version, supported features, secure partitions number and attributes.
Please refer to the following paragraphs for more details: [2], [3], [4], [5]
The core driver provided by this patchset implements the Setup and discovery interfaces in addition to direct messaging.
The driver provides ffa_bus_discover() API that allows to discover the FF-A bus as described by the spec and in the FF-A driver readme [6].
We expect and highly recommend FF-A users to always discover the FF-A bus using ffa_bus_discover() API.
Thanks for the details. But IIRC this discussion is not about the FF-A bus and device(partitions) discovery, but the support for FF-A itself. The discussion is about where to have a device node to represent the existence of FF-A support on a platform. If we are talking about individual partitions (devices) in the device tree, then that is pure stupidity as it goes out of since with the firmware the moment a partition is added or removed in the firmware.
IIUC, the whole discussion was around whether to use FFA_VERSION as the discovery mechanism for existence of FF-A support on a platform or you have a device node to specify the same.
No, with respect, that is not quite the situation here.
Just to be clear, even if it is decided to add a device node, the FFA_VERSION must be used to detect the presence of FF-A support and return error otherwise. DT node presence is just to satisfy the design and must be treated as no auto-confirmation for the presence of FF-A support. We are just arguing the device node presence is just redundant, but as mentioned before it is up to U-Boot community to make a call on what is best.
U-Boot driver model design already supports this. You can have a device that binds (from DT) but will not probe because it is not present / wrong version. Perhaps this was missed in the conversion to Linux:
https://u-boot.readthedocs.io/en/latest/develop/driver-model/design.html#dri...
So there is nothing clever needed here at all and anything you do just adds confusion and bad precedent.
Regards, Simon