On Monday, November 26, 2018 11:33:25 PM CET Moore, Robert wrote:
> Looks like another round of issues with the completely ill-defined generic serial bus. Below is a summary of the problems we have seen with the Length field.
>
> I have not had time to completely read through this thread yet, so I'm posting some text that I wrote a month or two ago.
>
> Let me say this, however:
>
> The biggest (and it is very big) issue is that the GenericSerialBus interfaces are so poorly defined in the ACPI specification that any implementation simply must guess at the proper behavior (Both the ACPI implementation and any related drivers).
OK, so what about the $subject patch?
Machines don't boot without it and that's rather serious, so I'm inclined to
apply it as a quick fix for 4.20, unless you have a better idea.
> Problems with these ACPI chapters:
> 5.5.2.4.6.2 Declaring and Using a GenericSerialBus Data Buffer
> 5.5.2.4.6.3 Using the GenericSerialBus Protocols
>
>
> 1) All of the ASL code examples do not compile due to syntax errors. There are
> 10 such examples, often with multiple syntax errors.
>
>
> 2) The basic/common data buffer format is not fully defined:
> typedef struct
> {
> BYTE Status; // Byte 0 of the data buffer
> BYTE Length; // Byte 1 of the data buffer
> BYTE[x-1] Data; // Bytes 2-x of the arbitrary length data buffer,
> } // where x is the last index of the overall buffer
>
> The "Length" field is not defined. Is it the length of "Data" or the Length of the entire structure (Status + Length + Data)?
>
> The example code from the spec illustrates how the "Length" term in the structure above is undefined. Again, is it the "length of entire structure" or is it the "length of the Data element"?. The example code makes it appear that it is the length of the entire structure, but it is not fully clear because it is wrong in either case:
>
> Name(BUFF, Buffer(34)()) // Create GenericSerialBus data buffer
> as BUFF
> CreateByteField(BUFF, 0x00, STAT) // STAT = Status (Byte)
> CreateByteField(BUFF, 0x01, LEN) // LEN = Length (Byte)
> CreateField(BUFF, 0x10, 256, DATA) // Data (Block)
>
> Store("ACPI", DATA) // Fill in outgoing data
> Store(8, LEN) // Length of the valid data
> (Actually should be 6? Or should it be 4?)
>
>
>
