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

Adriana Kobylak anoo at linux.vnet.ibm.com
Thu Oct 12 09:07:37 AEDT 2017


Acked-by: Adriana Kobylak <anoo at us.ibm <mailto:anoo at us.ibm.com>.com <mailto:anoo at us.ibm.com>>

> On Oct 5, 2017, at 1:10 AM, Andrew Jeffery <andrew at aj.id.au> wrote:
> 
> 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
>> GET_FLASH_INFO, CREATE_{READ/WRITE}_WINDOW, and MARK_LOCKED commands now
>> 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>
> 
> Reviewed-by: Andrew Jeffery <andrew at aj.id.au <mailto:andrew at aj.id.au>>
> 
> But everyone else: please chime in.
> 
> Cheers,
> 
> Andrew
> 
>> ---
>>  Documentation/mbox_protocol.md | 163 ++++++++++++++++++++++++++++++++---------
>>  1 file changed, 127 insertions(+), 36 deletions(-)
>> 
>> diff --git a/Documentation/mbox_protocol.md b/Documentation/mbox_protocol.md
>> index bcd70a8..797ac7b 100644
>> --- a/Documentation/mbox_protocol.md
>> +++ b/Documentation/mbox_protocol.md
>> @@ -17,19 +17,22 @@ limitations under the License.
>>  This document describes a protocol for host to BMC communication via the
>>  mailbox registers present on the Aspeed 2400 and 2500 chips.
>>  This protocol is specifically designed to allow a host to request and manage
>> -access to the flash with the specifics of how the host is required to control
>> -this described below.
>> +access to a flash device(s) with the specifics of how the host is required to
>> +control this described below.
>>  
>>  ## Version
>>  
>> -Both version 1 and version 2 of the protocol are described below with version 2
>> -specificities represented with V2 in brackets - (V2).
>> +Version specific protocol functionalities are represented by the version number
>> +in brackets next to the definition of the functionality. (e.g. (V2) for version
>> +2 specific funtionality). All version specific functionality must also be
>> +implemented by proceeding versions up to and not including the version a command
>> +was removed.
>>  
>>  ## Problem Overview
>>  
>>  "mbox" is the name we use to represent a protocol we have established between
>>  the host and the BMC via the Aspeed mailbox registers. This protocol is used
>> -for the host to control the flash.
>> +for the host to control access to the flash device(s).
>>  
>>  Prior to the mbox protocol, the host uses a backdoor into the BMC address space
>>  (the iLPC-to-AHB bridge) to directly manipulate the BMCs own flash controller.
>> @@ -215,9 +218,11 @@ communicate a change in state.
>>  Given that a majority of command and response arguments are specified as a
>>  multiple of block size it is necessary for the host and BMC to agree on a
>>  protocol version as this determines the block size. In V1 it is hard coded at
>> -4K and in V2 the BMC chooses and specifies this to the host as a response
>> -argument to `MBOX_GET_INFO`. Thus the host must always call `MBOX_GET_INFO`
>> -before any other command which specifies an argument in block size.
>> +4K, in V2 the BMC chooses and in V3 the host is allowed to request a specific
>> +block size with the actual size chosen communicated back to the host as a
>> +response argument to `MBOX_GET_INFO`. Thus the host must always call
>> +`MBOX_GET_INFO` before any other command which specifies an argument in block
>> +size.
>>  
>>  When invoking `MBOX_GET_INFO` the host must provide the BMC its highest
>>  supported version of the protocol. The BMC must respond with a protocol version
>> @@ -231,10 +236,13 @@ version by issuing a subsequent `MBOX_GET_INFO` command.
>>  ### Window Management
>>  
>>  In order to access flash contents, the host must request a window be opened at
>> -the flash offset it would like to access. The host may give a hint as to how
>> -much data it would like to access or otherwise set this argument to zero. The
>> -BMC must respond with the LPC bus address to access this window and the
>> -window size. The host must not access past the end of the active window.
>> +the flash offset it would like to access with the CREATE_{READ,WRITE}_WINDOW
>> +commands. The host may give a hint as to how much data it would like to access
>> +or otherwise set this argument to zero. The BMC must respond with the LPC bus
>> +address to access this window and the window size. The host must not access
>> +past the end of the active window. On returning success to either of the create
>> +window commands the BMC must guarantee that the window provided contains data
>> +which correctly represents the state of flash at the time the response is given.
>>  
>>  There is only ever one active window which is the window created by the most
>>  recent CREATE_READ_WINDOW or CREATE_WRITE_WINDOW call which succeeded. Even
>> @@ -278,7 +286,19 @@ contents cannot be guaranteed.
>>  
>>  The host is not required to perform an erase before a write command and the
>>  BMC must ensure that a write performs as expected - that is if an erase is
>> -required before a write then the BMC must perform this itself.
>> +required before a write then the BMC must perform this itself (unless the
>> +no_erase flag is set in the MARK_WRITE_DIRTY command in which case the BMC will
>> +blindly write without a prior erase (V3)).
>> +
>> +The host may lock an area of flash using the MARK_LOCKED command. Any attempt
>> +to mark dirty or erased this area of flash must fail with the LOCKED_ERROR
>> +response code. The host may open a write window which contains a locked area
>> +of flash however changes to a locked area of flash must never be written back
>> +to the backing data source (i.e. that area of flash must be treated as read
>> +only with respect to the backing store at all times). An attempt to lock an area
>> +of flash which is not clean in the current window must fail with PARAM_ERROR.
>> +Locked flash regions must persist across a BMC reboot or daemon restart. It is
>> +only possible to clear the lock state through a clear_locked dbus command. (V3)
>>  
>>  ### BMC Events
>>  
>> @@ -316,6 +336,8 @@ MARK_WRITE_DIRTY     0x07
>>  WRITE_FLUSH          0x08
>>  BMC_EVENT_ACK        0x09
>>>  MARK_WRITE_ERASED    0x0a	(V2)
>>> +GET_FLASH_NAME       0x0b	(V3)
>>> +MARK_LOCKED          0x0c	(V3)
>>  ```
>>  
>>  ### Responses
>>> @@ -329,13 +351,14 @@ TIMEOUT		5
>>>>  BUSY		6	(V2)
>>>>  WINDOW_ERROR	7	(V2)
>>>>  SEQ_ERROR	8	(V2)
>>>> +LOCKED_ERROR	9	(V3)
>>  ```
>>  
>>  ### Sequence Numbers
>>  
>>  Sequence numbers are included in messages for correlation of commands and
>> -responses. V1 and V2 of the protocol permit either zero or one commands to be
>> -in progress (yet to receive a response).
>> +responses. V1, V2 and V3 of the protocol permit either zero or one commands to
>> +be in progress (yet to receive a response).
>>  
>>  For generality, the host must generate a sequence number that is unique with
>>  respect to the previous command (one that has received a response) and any
>>> @@ -368,6 +391,10 @@ BUSY		- Daemon in suspended state (currently unable to access flash)
>>>  WINDOW_ERROR	- Command not valid for active window or no active window
>>>  		- Try opening an appropriate window and retrying the command
>>  
>>> +SEQ_ERROR	- Invalid sequence number supplied with command
>> +
>>> +LOCKED_ERROR	- Tried to mark dirty or erased locked area of flash
>> +
>>  ### Information
>>  - All multibyte messages are LSB first (little endian)
>>  - All responses must have a valid return code in byte 13
>> @@ -381,6 +408,12 @@ allows us to specify larger values with fewer command and response fields.
>>  
>>  In V1 block size is hard coded to 4K.
>>  In V2 it is variable and must be queried with the GET_MBOX_INFO command.
>> +In V3 the host can request a given block size however it is ultimately up to
>> +the daemon to choose a block size which is returned as part of the GET_MBOX_INFO
>> +command response. The host must respect the daemons choice. The ability for the
>> +host to request a block size is provided such that it can choose an appropriate
>> +size to be able to utilise commands which only operate at the block level.
>> +
>>  Note that for simplicity block size must always be a power-of-2.
>>  Block size must also be greater than or equal to 4K. This is due to the
>>  fact that we have a 28-bit LPC address space and commands which return an
>> @@ -395,8 +428,7 @@ multiplying by the block size.
>>  ```
>>  Command:
>>>  	RESET_STATE
>>> -	Implemented in Versions:
>>> -		V1, V2
>>>> +	Added in:	V1
>>>  	Arguments:
>>>  		-
>>>  	Response:
>> @@ -409,8 +441,7 @@ Command:
>>  
>>  Command:
>>>  	GET_MBOX_INFO
>>> -	Implemented in Versions:
>>> -		V1, V2
>>>> +	Added in:	V1
>>>  	Arguments:
>>>  		V1:
>>>  		Args 0: API version
>> @@ -418,6 +449,10 @@ Command:
>>>  		V2:
>>>  		Args 0: API version
>>  
>>> +		V3:
>>> +		Args 0: API version
>>> +		Args 1: Requested block size (shift)
>> +
>>>  	Response:
>>>  		V1:
>>>  		Args 0: API version
>> @@ -430,6 +465,14 @@ Command:
>>>  		Args 3-4: reserved
>>>  		Args 5: Block size as power of two (encoded as a shift)
>>>  		Args 6-7: Suggested Timeout (seconds)
>> +
>>> +		V3:
>>> +		Args 0: API version
>>> +		Args 1-2: reserved
>>> +		Args 3-4: reserved
>>> +		Args 5: Block size as power of two (encoded as a shift)
>>> +		Args 6-7: Suggested Timeout (seconds)
>>> +		Args 8: Num Allocated Flash IDs
>>>  	Notes:
>>>  		The suggested timeout is a hint to the host as to how long
>>>  		it should wait after issuing a command to the BMC before it
>> @@ -439,25 +482,34 @@ Command:
>>>>  		the BMC	does not wish to provide a hint in which case the host
>>>  		must choose some reasonable value.
>>  
>>> +		The host may desire a specific block size and thus can request
>>> +		this by giving a hint to the daemon (may be zero). The daemon
>>> +		may use this to select the block size which it will use however
>>> +		is free to ignore it. The value in the response is the block
>>> +		size which must be used for all further requests until a new
>>>> +		size is	negotiated by another call to GET_MBOX_INFO. (V3)
>> +
>>  Command:
>>>  	GET_FLASH_INFO
>>> -	Implemented in Versions:
>>> -		V1, V2
>>>> +	Added in:	V1
>>>  	Arguments:
>>> +		V1, V2:
>>>  		-
>> +
>>> +		V3:
>>> +		Args 0: Flash ID
>>>  	Response:
>>>  		V1:
>>>  		Args 0-3: Flash size (bytes)
>>>  		Args 4-7: Erase granule (bytes)
>>  
>>> -		V2:
>>> +		V2, V3:
>>>  		Args 0-1: Flash size (blocks)
>>>  		Args 2-3: Erase granule (blocks)
>>  
>>  Command:
>>>  	CREATE_{READ/WRITE}_WINDOW
>>> -	Implemented in Versions:
>>> -		V1, V2
>>>> +	Added in:	V1
>>>  	Arguments:
>>>  		V1:
>>>  		Args 0-1: Requested flash offset (blocks)
>> @@ -466,11 +518,15 @@ Command:
>>>  		Args 0-1: Requested flash offset (blocks)
>>>  		Args 2-3: Requested flash size to access (blocks)
>>  
>>> +		V3:
>>> +		Args 0-1: Requested flash offset (blocks)
>>> +		Args 2-3: Requested flash size to access (blocks)
>>> +		Args 4: Flash ID
>>>  	Response:
>>>  		V1:
>>>  		Args 0-1: LPC bus address of window (blocks)
>>  
>>> -		V2:
>>> +		V2, V3:
>>>  		Args 0-1: LPC bus address of window (blocks)
>>>  		Args 2-3: Window size (blocks)
>>>  		Args 4-5: Flash offset mapped by window (blocks)
>> @@ -505,8 +561,7 @@ Command:
>>  
>>  Command:
>>>  	CLOSE_WINDOW
>>> -	Implemented in Versions:
>>> -		V1, V2
>>>> +	Added in:	V1
>>>  	Arguments:
>>>  		V1:
>>>  		-
>> @@ -534,8 +589,7 @@ Command:
>>  
>>  Command:
>>>  	MARK_WRITE_DIRTY
>>> -	Implemented in Versions:
>>> -		V1, V2
>>>> +	Added in:	V1
>>>  	Arguments:
>>>  		V1:
>>>  		Args 0-1: Flash offset to mark from base of flash (blocks)
>> @@ -544,6 +598,7 @@ Command:
>>>  		V2:
>>>  		Args 0-1: Window offset to mark (blocks)
>>>  		Args 2-3: Number to mark dirty at offset (blocks)
>>> +		Args 4  : Don't Erase Before Write (V3)
>>  
>>>  	Response:
>>>  		-
>> @@ -558,10 +613,16 @@ Command:
>>>  		block. If the offset + number exceeds the size of the active
>>>  		window then the command must not succeed.
>>  
>>> +		The host can give a hint to the daemon that is doesn't have to
>>> +		erase a flash area before writing to it by setting ARG[4]. This
>>> +		means that the daemon will blindly perform a write to that area
>>> +		and will not try to erase it before hand. This can be used if
>>> +		the host knows that a large area has already been erased for
>>> +		example but then wants to perform many small writes.
>> +
>>  Command
>>>  	WRITE_FLUSH
>>> -	Implemented in Versions:
>>> -		V1, V2
>>>> +	Added in:	V1
>>>  	Arguments:
>>>  		V1:
>>>  		Args 0-1: Flash offset to mark from base of flash (blocks)
>> @@ -586,8 +647,7 @@ Command
>>  
>>  Command:
>>>  	BMC_EVENT_ACK
>>> -	Implemented in Versions:
>>> -		V1, V2
>>>> +	Added in:	V1
>>>  	Arguments:
>>>>  		Args 0:	Bits in the BMC status byte (mailbox data
>>>  			register 15) to ack
>> @@ -599,8 +659,7 @@ Command:
>>  
>>  Command:
>>>  	MARK_WRITE_ERASED
>>> -	Implemented in Versions:
>>> -		V2
>>>> +	Added in:	V2
>>>  	Arguments:
>>>  		V2:
>>>  		Args 0-1: Window offset to erase (blocks)
>> @@ -617,6 +676,38 @@ Command:
>>>  		number is the number of blocks of the active window to erase
>>>  		starting at offset. If the offset + number exceeds the size of
>>>  		the active window then the command must not succeed.
>> +
>> +Command:
>>> +	GET_FLASH_NAME
>>>> +	Added in:	V3
>>> +	Arguments:
>>> +		Args 0: Flash ID
>>> +	Response:
>>> +		Args 0   : Flash Name Length (bytes)
>>> +		Args 1-10: Flash Name / UID
>>> +	Notes:
>>> +		Describes a flash with some kind of identifier useful to the
>>> +		host system. This is typically a null-padded string.
>> +
>>> +		The length in the response is the number of response arguments
>>> +		as part of the flash name field which the host should expect to
>>> +		have been populated.
>> +
>> +Command:
>>> +	MARK_LOCKED
>>>> +	Added in:	V3
>>> +	Arguments:
>>> +		Args 0-1: Flash offset to lock (blocks)
>>> +		Args 2-3: Number to lock at offset (blocks)
>>> +		Args 4: Flash ID
>>> +	Response:
>>> +		-
>>> +	Notes:
>>> +		Lock an area of flash so that the host can't mark it dirty or
>>> +		erased. If the requested area is within the current window and
>>> +		that area is currently marked dirty or erased then this command
>>> +		must fail with PARAM_ERROR.
>> +
>>  ```
>>  
>>  ### BMC Events in Detail:
>> @@ -627,7 +718,7 @@ on that register, or otherwise be polling it.
>>  
>>  #### Bit Definitions:
>>  
>> -Events which should be ACKed:
>> +Events which must be ACKed:
>>  ```
>>  0x01: BMC Reboot
>>  0x02: BMC Windows Reset (V2)

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