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Subject: Re: [PATCH v3] virtio-i2c: add the device specification
On Tue, Oct 27, 2020 at 02:00:24PM +0800, Jie Deng wrote: > virtio-i2c is a virtual I2C adapter device. It provides a way > to ïexibly communicate with the I2C slave devices from the guest. > > This patch adds the specification for this device. > > Signed-off-by: Jie Deng <jie.deng@intel.com> > --- > conformance.tex | 28 ++++++++++++++--- > content.tex | 1 + > virtio-i2c.tex | 94 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > 3 files changed, 119 insertions(+), 4 deletions(-) > create mode 100644 virtio-i2c.tex > > diff --git a/conformance.tex b/conformance.tex > index f1f23a8..12bce3a 100644 > --- a/conformance.tex > +++ b/conformance.tex > @@ -27,8 +27,10 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets} > \ref{sec:Conformance / Driver Conformance / Socket Driver Conformance}, > \ref{sec:Conformance / Driver Conformance / RPMB Driver Conformance}, > \ref{sec:Conformance / Driver Conformance / IOMMU Driver Conformance}, > -\ref{sec:Conformance / Driver Conformance / Sound Driver Conformance} or > -\ref{sec:Conformance / Driver Conformance / Memory Driver Conformance}. > +\ref{sec:Conformance / Driver Conformance / Sound Driver Conformance} > +\ref{sec:Conformance / Driver Conformance / Memory Driver Conformance} or > +\ref{sec:Conformance / Driver Conformance / I2C Adapter Driver Conformance}. > + > \item Clause \ref{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance}. > \end{itemize} > \item[Device] A device MUST conform to four conformance clauses: > @@ -47,8 +49,10 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets} > \ref{sec:Conformance / Device Conformance / Socket Device Conformance}, > \ref{sec:Conformance / Device Conformance / RPMB Device Conformance}, > \ref{sec:Conformance / Device Conformance / IOMMU Device Conformance}, > -\ref{sec:Conformance / Device Conformance / Sound Device Conformance} or > -\ref{sec:Conformance / Device Conformance / Memory Device Conformance}. > +\ref{sec:Conformance / Device Conformance / Sound Device Conformance} > +\ref{sec:Conformance / Device Conformance / Memory Device Conformance} or > +\ref{sec:Conformance / Device Conformance / I2C Adapter Device Conformance}. > + > \item Clause \ref{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance}. > \end{itemize} > \end{description} > @@ -261,6 +265,14 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets} > \item \ref{drivernormative:Device Types / Memory Device / Device Operation / STATE request} > \end{itemize} > > +\conformance{\subsection}{I2C Adapter Driver Conformance}\label{sec:Conformance / Driver Conformance / I2C Adapter Driver Conformance} > + > +An I2C Adapter driver MUST conform to the following normative statements: > + > +\begin{itemize} > +\item \ref{drivernormative:Device Types / I2C Adapter Device / Device Operation} > +\end{itemize} > + > \conformance{\section}{Device Conformance}\label{sec:Conformance / Device Conformance} > > A device MUST conform to the following normative statements: > @@ -477,6 +489,14 @@ \section{Conformance Targets}\label{sec:Conformance / Conformance Targets} > \item \ref{devicenormative:Device Types / Memory Device / Device Operation / STATE request} > \end{itemize} > > +\conformance{\subsection}{I2C Adapter Device Conformance}\label{sec:Conformance / Device Conformance / I2C Adapter Device Conformance} > + > +An I2C Adapter device MUST conform to the following normative statements: > + > +\begin{itemize} > +\item \ref{devicenormative:Device Types / I2C Adapter Device / Device Operation} > +\end{itemize} > + > \conformance{\section}{Legacy Interface: Transitional Device and Transitional Driver Conformance}\label{sec:Conformance / Legacy Interface: Transitional Device and Transitional Driver Conformance} > A conformant implementation MUST be either transitional or > non-transitional, see \ref{intro:Legacy > diff --git a/content.tex b/content.tex > index 91855b4..95e2ed8 100644 > --- a/content.tex > +++ b/content.tex > @@ -6200,6 +6200,7 @@ \subsubsection{Legacy Interface: Framing Requirements}\label{sec:Device > \input{virtio-iommu.tex} > \input{virtio-sound.tex} > \input{virtio-mem.tex} > +\input{virtio-i2c.tex} > > \chapter{Reserved Feature Bits}\label{sec:Reserved Feature Bits} > > diff --git a/virtio-i2c.tex b/virtio-i2c.tex > new file mode 100644 > index 0000000..96c96bf > --- /dev/null > +++ b/virtio-i2c.tex > @@ -0,0 +1,94 @@ > +\section{I2C Adapter Device}\label{sec:Device Types / I2C Adapter Device} > + > +virtio-i2c is a virtual I2C adapter device. It provides a way to flexibly > +organize and manage I2C slave devices from the guest. By attaching ACPI > +I2C slave nodes to the virtual I2C adapter device, the guest can > +communicate with them without changing or adding extra drivers for these > +slave I2C devices. > + > +\subsection{Device ID}\label{sec:Device Types / I2C Adapter Device / Device ID} > +34 > + > +\subsection{Virtqueues}\label{sec:Device Types / I2C Adapter Device / Virtqueues} > + > +\begin{description} > +\item[0] requestq > +\end{description} > + > +\subsection{Feature bits}\label{sec:Device Types / I2C Adapter Device / Feature bits} > + > +None currently defined. > + > +\subsection{Device configuration layout}\label{sec:Device Types / I2C Adapter Device / Device configuration layout} > + > +None currently defined. > + > +\subsection{Device Initialization}\label{sec:Device Types / I2C Adapter Device / Device Initialization} > + > +\begin{enumerate} > +\item The virtqueue is initialized. > +\end{enumerate} > + > +\subsection{Device Operation}\label{sec:Device Types / I2C Adapter Device / Device Operation} > + > +The driver queues requests to the virtqueue, and they are used by the > +device. The request is the representation of one segment of an I2C > +transaction. Each request is of form: > + > +\begin{lstlisting} > +struct virtio_i2c_req { > + le16 addr; > + le16 flags; > + le16 len; > + u8 buf[]; > + u8 status; > +}; > +\end{lstlisting} > + > +The \field{addr} is the address of the I2C slave device. > + > +The first bit of \field{flags} indicates whether it is a read or write request. > +It means a read request if the first bit of \field{flags} is set, otherwise > +it is a write request. The rest bits of \field{flags} are reserved. > + > +The \field{len} is the number of data bytes in the \field{buf} being read from or > +written to the I2C slave address. > + > +The \field{buf} of the request contains one segment of an I2C transaction. > +If the first bit of \field{flags} is '1', the \field{buf} is written by the > +device and it contains one segment of an I2C transaction being read from the > +device. Let's give a name to the flag then? READ I guess? I guess this means it's an exact reverse of the write-only/read-only flag in the descriptor? I still think it's both a potential source of errors and a waste to have this bit in the device struct when we have a generic one. How about adding some motivation to explain why it's done like this? > If the first bit of \field{flags} is '0', the \field{buf} is written > +by the driver and it contains one segment of an I2C transaction being written > +to the the device. one the? more detail on how are multi-segment transactions formed? don't you need flags to start/stop? > +The final \field{status} byte is written by the device: either VIRTIO_I2C_MSG_OK > +for success or VIRTIO_I2C_MSG_ERR for error. > + > +\begin{lstlisting} > +#define VIRTIO_I2C_MSG_OK 0 > +#define VIRTIO_I2C_MSG_ERR 1 > +\end{lstlisting} what if one segment in a transaction fails? > +\drivernormative{\subsubsection}{Device Operation}{Device Types / I2C Adapter Device / Device Operation} > + > +A driver MUST set \field{addr}, \field{flags} and \field{len} before sending > +the request. > + > +A driver MUST place one segment of an I2C transaction into \field{buf} if the > +first bit of \field{flags} is '0'. > + > +A driver MUST NOT use \field{addr}, \field{flags}, \field{len} and \field{buf} > +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. > + > +\devicenormative{\subsubsection}{Device Operation}{Device Types / I2C Adapter Device / Device Operation} > + > +A device MUST NOT change the value of \field{addr}, \field{flags} and \field{len}. > + > +A device MUST place one segment of an I2C transaction into \field{buf} if the first > +bit of \field{flags} is '1'. > + > +A device MUST guarantee the requests being handled in order if multiple requests > +are received. > -- > 2.7.4
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