[Skiboot] [PATCH] docs: Specify V3 of the mbox protocol

Andrew Jeffery andrew at aj.id.au
Fri Oct 13 16:13:25 AEDT 2017

On Wed, 2017-10-04 at 11:45 +1100, Suraj Jitindar Singh wrote:
> Version 3 of the mbox protocol makes four protocol changes:
>  - Add a requested block size argument to GET_MBOX_INFO
>  - Add a no erase argument to MARK_DIRTY
>  - Add a GET_FLASH_NAME command and support multiple flash devices
>  - Add a MARK_LOCKED command
> Requested Block Size:
> The requested block size argument has been added to the GET_MBOX_INFO
> command to allow the host to request a specified block size which might
> be required to allow data manipulation at a finer granularity. The
> daemon should take this into account when choosing a block size for use
> which it will specify in the response as before. The daemon has final
> say and the host must use the block size the daemon chooses.
> No Erase:
> The no erase argument to the mark dirty command allows a host to specify
> that an area of flash should not be erased before being written to, as is
> the default behaviour. This can be used when a host has already erased a
> large area and then performs many small writes which would normally mean
> many erases due to the implicit erase before write, making this slow.
> Add GET_FLASH_NAME command:
> The ability to support multiple flash devices has been added so that the
> mbox protocol can be used to arbitrate access from the host to a number
> of flash devices which the daemon has access to. To facilitate this the
> take a flash ID, with the number of flash IDs allocated returned by the
> GET_MBOX_INFO commands. There is also a new command GET_FLASH_NAME used
> to convert a flash ID to a flash name.
> Add MARK_LOCKED command:
> The MARK_LOCKED command has been added to allow an area(s) of flash to be
> locked, that is that area must be treated as read only and the host is
> not allowed to dirty or erase any windows which map that area of flash.
> Additionally another error code LOCKED_ERROR was added to be returned
> when the host does try to dirty or erase a locked area.
> The host cannot lock a currently dirty or erased area of the current
> write window as it is not defined if the clean/dirty/erased value is
> what should actually be "locked".
> A locked area of flash remains so until the daemon receives an
> mboxctl --clear-locked command and the locked areas are stored in a file
> on the BMC filesystem to ensure persistence across BMC reboots/daemon
> crashes.
> Multiple flash device support proposed and defined by:
> William A. Kennington III <wak at google.com>
> Change-Id: I898698840dec221ae20e33943bb28e65abc4fe37
> Signed-off-by: Suraj Jitindar Singh <sjitindarsingh at gmail.com>

William - any chance you can ack/review this?


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