On Wed, Jan 18, 2023 at 08:59:32AM -0500, Tom Rini wrote: > On Wed, Jan 18, 2023 at 01:46:54PM +0000, Sudeep Holla wrote: > > On Wed, Jan 18, 2023 at 12:49 PM Tom Rini <tr...@konsulko.com> wrote: > > > > > > > > I guess the problem comes down to, can we have one discovery method that > > > everyone shares, or do we have to let everyone invent a new discovery > > > method every time? > > > > > > No one needs to invent any discovery method every time if the firmware > > specification > > provides one and as Rob mentioned many times in the thread, all new firmware > > specification must provide one and we are trying to make sure that is > > the case with all new > > specs from Arm. > > > > > > > FF-A, Op-tee, U-Boot, coreboot, barebox (and > > > everyone else I'm unintentionally forgetting) could just discover these > > > things via device tree. > > > > > > I leave that to the individual projects to decide and agree but > > fundamentally if > > the specification provides a way to discover, not sure why we are even > > discussing > > an alternative method here. > > > > > > > Or, we could all write our own code to perform > > > the discovery. > > > > > > For what reason ? I can understand if there is no discovery mechanism but > > that's not the > > case in $subject. > > > > > > > And when RISC-V comes along with similar functionality, > > > we could probe their device tree and see they've implemented the same > > > concept, but a little differently, but still have the discovery portion > > > be in the device tree. To which it sounds like your answer is "not in > > > the device tree". > > > > > > > I see U-boot seem to have made a decision to create DT node for each and > > everything > > that needs to be added to DM which seems bit unfortunate but I don't > > understand the > > history/motive/background for it but I respect the decision if it is > > already made. > > > > These firmware interfaces are standard on all Arm platforms and can be > > discovered > > based on PSCI/SMCCC. Not using the same and use DT node needs unnecessary > > addition of DT nodes for all the f/w i/f on all the platforms that need the > > support when > > one can be just discovered. > > > > Sorry for the sudden appearance on this thread, I was avoiding getting into > > this but thought > > I will at least express my opinion and also the way the firmware > > specifications from Arm is > > expected to be evolved from now on. With that I will leave it to you and > > other U-boot > > maintainers and the community in general to decide the right course in this > > case. > > To be clear, if the position is that "this is what everyone else will > use, really" then yes, we'll follow this in U-Boot.
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. A use case is provided which is the EFI MM communication [7]. ffa_bus_discover() does the following: - creates, binds and probes the arm_ffa device - at probe level, discovery FF-A interfaces are called to try to discover the FF-A framework - when all discovery interfaces succeed, probing is successful and FF-A bus is ready to use - if one of the discovery interfaces fails, the arm_ffa device is removed from the DM and FF-A bus can not be used Cheers Abdellatif [1]: FF-A spec version 1.0, https://developer.arm.com/documentation/den0077/latest/ [2] 2.8 Partition identification and discovery All FF-A components can discover the identities and properties of other partitions through the FFA_PARTITION_INFO_GET interface. Once discovered, the IDs must be used in the messaging interfaces to identify the target of a message. [3] 4.2.2.2 Buffer discovery and setup This version of the Framework enables discovery and setup of RX/TX buffer pairs between FF-A components as follows. ... 2. An endpoint could allocate the buffer pair and use the FFA_RXTX_MAP interface to map it with the Hypervisor or SPM as applicable. [4] 4.2.2.3 Buffer attributes An endpoint must discover the minimum size and alignment boundary for the RX/TX buffers by passing the function ID of the FFA_RXTX_MAP ABI as input in the FFA_FEATURES interface (see 8.2 FFA_FEATURES). [5] 6.1.1 Common compliance requirements - It must be possible for the FF-A components at an FF-A instance to discover the presence and version number of their Framework implementations through the FFA_VERSION interface (see 8.1 FFA_VERSION). - All FF-A components must implement support for Setup and discovery interfaces described in Chapter 8 Setup and discovery interfaces. These interfaces are as follows. FFA_VERSION. FFA_FEATURES. FFA_RX_RELEASE. FFA_RXTX_MAP. FFA_RXTX_UNMAP. FFA_PARTITION_INFO_GET. FFA_ID_GET. - It must be possible for an FF-A component, at the lower EL at an FF-A instance to use the FFA_FEATURES interface (see 8.2 FFA_FEATURES) to discover if an FF-A interface is implemented by the FF-A component at the higher EL. [6] FF-A support readme: https://lore.kernel.org/all/20221122131751.22747-4-abdellatif.elkhl...@arm.com/#Z31doc:arch:arm64.ffa.rst [7] FF-A MM comms: https://lore.kernel.org/all/20221122131751.22747-10-abdellatif.elkhl...@arm.com/ > > -- > Tom