[PATCH v16 09/10] arm_ffa: efi: introduce FF-A MM communication

[Abdellatif El Khlifi]

Hi Tom,

On Wed, Jul 26, 2023 at 03:39:12PM -0400, Tom Rini wrote:
> On Wed, Jul 26, 2023 at 10:45:02AM +0100, Abdellatif El Khlifi wrote:
> 
> > Add MM communication support using FF-A transport
> > 
> > This feature allows accessing MM partitions services through
> > EFI MM communication protocol. MM partitions such as StandAlonneMM
> > or smm-gateway secure partitions which reside in secure world.
> > 
> > An MM shared buffer and a door bell event are used to exchange
> > the data.
> > 
> > The data is used by EFI services such as GetVariable()/SetVariable()
> > and copied from the communication buffer to the MM shared buffer.
> > 
> > The secure partition is notified about availability of data in the
> > MM shared buffer by an FF-A message (door bell).
> > 
> > On such event, MM SP can read the data and updates the MM shared
> > buffer with the response data.
> > 
> > The response data is copied back to the communication buffer and
> > consumed by the EFI subsystem.
> > 
> > MM communication protocol supports FF-A 64-bit direct messaging.
> > 
> > Signed-off-by: Abdellatif El Khlifi <abdellatif.elkhlifi at arm.com>
> > Tested-by: Gowtham Suresh Kumar <gowtham.sureshkumar at arm.com>
> > Reviewed-by: Simon Glass <sjg at chromium.org>
> > Cc: Tom Rini <trini at konsulko.com>
> > Cc: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> > Cc: Jens Wiklander <jens.wiklander at linaro.org>
> 
> So, at this point in the series we impact lx2160ardb_tfa_stmm which is
> the only config in the tree prior to this series that sets
> CONFIG_EFI_MM_COMM_TEE. I'm not going to block this series[1] on
> updating lx2160ardb_tfa_stmm as well, but I do want to make sure the
> maintainers there are aware and can update the config to support the
> current state of this technology.
> 
> [1]: https://patchwork.ozlabs.org/project/uboot/list/?series=365876&state=*
> -- 

Following a decision made with Ilias, the new MM comms design works as follows:

- Try to communicate using FF-A bus first
- If that fails, try to communicate using Optee. So, platforms that don't support FF-A
  in the Secure side can still use Optee communication

This is done through the code below [1].

This logic needs CONFIG_ARM_FFA_TRANSPORT=y in the defconfig.

I added CONFIG_ARM_FFA_TRANSPORT=y to lx2160ardb_tfa_stmm_defconfig, CONFIG_EFI_MM_COMM_TEE is enabled and it builds fine.

Is it expected that lx2160ardb_tfa_stmm maintainers add CONFIG_ARM_FFA_TRANSPORT=y to lx2160ardb_tfa_stmm_defconfig ?

Cheers
Abdellatif

[1]: Selecting the MM comms method:

static efi_status_t mm_communicate(u8 *comm_buf, efi_uintn_t dsize)
...
	mm_comms = get_mm_comms();
	if (mm_comms == MM_COMMS_FFA)
		ret = ffa_mm_communicate(comm_buf, dsize);
	else
		ret = optee_mm_communicate(comm_buf, dsize);