The virtio I2C protocol allows to contain multiple read-write requests in a single I2C transaction using the VIRTIO_I2C_FLAGS_FAIL_NEXT flag, where each request contains a header, buffer and status.
There is no need to pass both read and write buffers in a single request, as we have a better way of combining requests into a single I2C transaction. Moreover, this also limits the transactions to two buffers, one for read operation and one for write. By using VIRTIO_I2C_FLAGS_FAIL_NEXT, we don't have any such limits.
Remove support for multiple buffers within a single request.
Fixes: https://github.com/oasis-tcs/virtio-spec/issues/112 Reviewed-by: Arnd Bergmann arnd@arndb.de Reviewed-by: Jie Deng jie.deng@intel.com Signed-off-by: Viresh Kumar viresh.kumar@linaro.org --- virtio-i2c.tex | 54 +++++++++++++++++++------------------------------- 1 file changed, 20 insertions(+), 34 deletions(-)
diff --git a/virtio-i2c.tex b/virtio-i2c.tex index 949d75f44158..5d634aec6e7c 100644 --- a/virtio-i2c.tex +++ b/virtio-i2c.tex @@ -54,8 +54,7 @@ \subsubsection{Device Operation: Request Queue}\label{sec:Device Types / I2C Ada \begin{lstlisting} struct virtio_i2c_req { struct virtio_i2c_out_hdr out_hdr; - u8 write_buf[]; - u8 read_buf[]; + u8 buf[]; struct virtio_i2c_in_hdr in_hdr; }; \end{lstlisting} @@ -89,11 +88,8 @@ \subsubsection{Device Operation: Request Queue}\label{sec:Device Types / I2C Ada Other bits of \field{flags} are currently reserved as zero for future feature extensibility.
-The \field{write_buf} of the request contains one segment of an I2C transaction -being written to the device. - -The \field{read_buf} of the request contains one segment of an I2C transaction -being read from the device. +The \field{buf} of the request contains one segment of an I2C transaction +being read from or written to the device.
The final \field{status} byte of the request is written by the device: either VIRTIO_I2C_MSG_OK for success or VIRTIO_I2C_MSG_ERR for error. @@ -103,27 +99,18 @@ \subsubsection{Device Operation: Request Queue}\label{sec:Device Types / I2C Ada #define VIRTIO_I2C_MSG_ERR 1 \end{lstlisting}
-If ``length of \field{read_buf}''=0 and ``length of \field{write_buf}''>0, -the request is called write request. - -If ``length of \field{read_buf}''>0 and ``length of \field{write_buf}''=0, -the request is called read request. - -If ``length of \field{read_buf}''>0 and ``length of \field{write_buf}''>0, -the request is called write-read request. It means an I2C write segment followed -by a read segment. Usually, the write segment provides the number of an I2C -controlled device register to be read. - -The case when ``length of \field{write_buf}''=0, and at the same time, -``length of \field{read_buf}''=0 doesn't make any sense. +The virtio I2C protocol supports write-read requests, i.e. an I2C write segment +followed by a read segment (usually, the write segment provides the number of an +I2C controlled device register to be read), by grouping a list of requests +together using the \field{VIRTIO_I2C_FLAGS_FAIL_NEXT} flag.
\subsubsection{Device Operation: Operation Status}\label{sec:Device Types / I2C Adapter Device / Device Operation: Operation Status}
-\field{addr}, \field{flags}, ``length of \field{write_buf}'' and ``length of \field{read_buf}'' -are determined by the driver, while \field{status} is determined by the processing -of the device. A driver puts the data written to the device into \field{write_buf}, while -a device puts the data of the corresponding length into \field{read_buf} according to the -request of the driver. +\field{addr}, \field{flags}, and ``length of \field{buf}'' are determined by the +driver, while \field{status} is determined by the processing of the device. A +driver, for a write request, puts the data to be written to the device into the +\field{buf}, while a device, for a read request, puts the data read from device +into the \field{buf} according to the request from the driver.
A driver may send one request or multiple requests to the device at a time. The requests in the virtqueue are both queued and processed in order. @@ -141,11 +128,8 @@ \subsubsection{Device Operation: Operation Status}\label{sec:Device Types / I2C
A driver MUST set the reserved bits of \field{flags} to be zero.
-The driver MUST NOT send a request with ``length of \field{write_buf}''=0 and -``length of \field{read_buf}''=0 at the same time. - -A driver MUST NOT use \field{read_buf} if the final \field{status} returned -from the device is VIRTIO_I2C_MSG_ERR. +A driver MUST NOT use \field{buf}, for a read request, if the final +\field{status} returned from the device is VIRTIO_I2C_MSG_ERR.
A driver MUST queue the requests in order if multiple requests are going to be sent at a time. @@ -160,11 +144,13 @@ \subsubsection{Device Operation: Operation Status}\label{sec:Device Types / I2C A device SHOULD keep consistent behaviors with the hardware as described in \hyperref[intro:I2C]{I2C}.
-A device MUST NOT change the value of \field{addr}, reserved bits of \field{flags} -and \field{write_buf}. +A device MUST NOT change the value of \field{addr}, and reserved bits of +\field{flags}. + +A device MUST not change the value of the \field{buf} for a write request.
-A device MUST place one I2C segment of the corresponding length into \field{read_buf} -according the driver's request. +A device MUST place one I2C segment of the ``length of \field{buf}'', for the +read request, into the \field{buf} according the driver's request.
A device MUST guarantee the requests in the virtqueue being processed in order if multiple requests are received at a time.