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Subject: Re: [virtio-dev] [PATCH V6 2/2] virtio-spi: add the device specification
On 30-11-23, 17:22, Haixu Cui wrote:
> The Virtio SPI (Serial Peripheral Interface) device is a virtual
> SPI controller that allows the driver to operate and use the SPI
> controller under the control of the device.
>
> This patch adds the specification for virtio-spi.
>
> Signed-off-by: Haixu Cui <quic_haixcui@quicinc.com>
> ---
> device-types/spi/description.tex | 288 ++++++++++++++++++++++++
> device-types/spi/device-conformance.tex | 7 +
> device-types/spi/driver-conformance.tex | 7 +
> 3 files changed, 302 insertions(+)
> create mode 100644 device-types/spi/description.tex
> create mode 100644 device-types/spi/device-conformance.tex
> create mode 100644 device-types/spi/driver-conformance.tex
>
> diff --git a/device-types/spi/description.tex b/device-types/spi/description.tex
> new file mode 100644
> index 0000000..c4816a6
> --- /dev/null
> +++ b/device-types/spi/description.tex
> @@ -0,0 +1,288 @@
> +\section{SPI Controller Device}\label{sec:Device Types / SPI Controller Device}
> +
> +The Virtio SPI (Serial Peripheral Interface) device is a virtual SPI controller that
> +allows the driver to operate and use the SPI controller under the control of the device,
s/control of the device/control of the host/
The host emulates and provides the guest with a device. 'device' is not really a
replacement for the word 'host`, but should be used to refer to the entity
emulated by the host.
> +either a physical SPI controller, or an emulated one.
> +
> +The Virtio SPI device has a single virtqueue. SPI transfer requests are placed into
> +the virtqueue, and serviced by the device.
s/the virtqueue, and /the virtqueue by the driver, and are /
> +
> +\subsection{Device ID}\label{sec:Device Types / SPI Controller Device / Device ID}
> +45
> +
> +\subsection{Virtqueues}\label{sec:Device Types / SPI Controller Device / Virtqueues}
> +
> +\begin{description}
> +\item[0] requestq
> +\end{description}
> +
> +\subsection{Feature bits}\label{sec:Device Types / SPI Controller Device / Feature bits}
> +
> +None
> +
> +\subsection{Device configuration layout}\label{sec:Device Types / SPI Controller Device / Device configuration layout}
> +
> +All fields of this configuration are always available and read-only for Virtio SPI driver.
s/always available/mandatory/
and "the Virtio SPI driver", everywhere else too..
> +The config space shows the features and settings supported by the device.
> +
> +\begin{lstlisting}
> +struct virtio_spi_config {
> + u8 cs_max_number;
> + u8 cs_change_supported;
> + u8 tx_nbits_supported;
> + u8 rx_nbits_supported;
> + le32 bits_per_word_mask;
> + le32 mode_func_supported;
> + le32 max_freq_hz;
> + le32 max_word_delay_ns;
> + le32 max_cs_setup_ns;
> + le32 max_cs_hold_ns;
> + le32 max_cs_inactive_ns;
> +};
> +\end{lstlisting}
> +
> +\field{cs_max_number} is the maximum number of chipselect the device supports.
> +
> +Note: chipselect is an electrical signal controlled by the SPI controller, used to select the
> +SPI slaves connected to the controller.
It isn't mandatory for the CS to be controlled by the controller. It can also be
a GPIO pin too which is controlled by the host driver.
Suggest rewriting as:
Note: chipselect is an electrical signal, which is used to select the SPI slaves
connected to the controller.
> +\field{cs_change_supported} indicates if the device supports to toggle chipselect
> +after each transfer in one message:
> + 0: unsupported, means chipselect will keep active when executing the message transaction;
0: unsupported, chipselect will be kept in active state throughout the transaction;
> + 1: supported.
> +
> +Note: Message here contains a sequence of SPI transfers.
> +
> +\field{tx_nbits_supported} indicates the supported number of bit for writing, SINGLE is always
> +supported. In the bit definition below, a set bit means the transfer is supported, otherwise not:
> + bit 0: DUAL;
> + bit 1: QUAD;
> + bit 2: OCTAL;
> + other bits are reserved and must be set to 0 by the device.
> +
Not sure if the below Note and the item list is required at all.
> +Note: Transfer bit options are commonly used in SPI:
> +\begin{itemize}
> +\item SINGLE: 1-bit transfer
> +\item DUAL: 2-bit transfer
> +\item QUAD: 4-bit transfer
> +\item OCTAL: 8-bit transfer
> +\end{itemize}
> +
> +\field{rx_nbits_supported} indicates the supported number of bit for reading, SINGLE is always
> +supported. In the bit definition below, a set bit means the transfer is supported, otherwise not:
> + bit 0: DUAL;
> + bit 1: QUAD;
> + bit 2: OCTAL;
> + other bits are reserved and must be set to 0 by the device.
> +
There is still some duplication left here in tx and rx bits supported fields.
Maybe rewrite the whole thing as:
"
\field{tx_nbits_supported} and \field{rx_nbits_supported} indicate the different
n-bit transfer modes supported by the device. The 1-bit transfer mode is always
supported. A set bit here indicates that the corresponding mode is supported,
otherwise not:
bit 0: DUAL;
bit 1: QUAD;
bit 2: OCTAL;
other bits are reserved and must be set to 0 by the device.
"
> +\field{bits_per_word_mask} is a mask indicating which values of bits_per_word are supported.
> +If not set, no limitation for bits_per_word.
> +
> +Note: bits_per_word corresponds to \field{bits_per_word} in \field{struct virtio_spi_transfer_head}.
> +
> +\field{mode_func_supported} indicates whether the following features are supported or not:
> + bit 0-1: CPHA feature,
> + 0b00: supports CPHA=0 and CPHA=1;
> + 0b01: supports CPHA=0 only;
> + 0b10: supports CPHA=1 only;
> + 0b11: invalid, must support as least one CPHA setting.
> +
> + bit 2-3: CPOL feature,
> + 0b00: supports CPOL=0 and CPOL=1;
> + 0b01: supports CPOL=0 only;
> + 0b10: supports CPOL=1 only;
> + 0b11: invalid, must support as least one CPOL setting.
> +
> + bit 4: chipselect active high feature, 0 for unsupported and 1 for supported,
> + chipselect active low must always be supported.
> +
> + bit 5: LSB first feature, 0 for unsupported and 1 for supported, MSB first must always be
> + supported.
> +
> + bit 6: loopback mode feature, 0 for unsupported and 1 for supported, normal mode
> + must always be supported.
> +
> +Note: CPOL is clock polarity and CPHA is clock phase. If CPOL is 0, clock idles at the logical
> +low voltage, otherwise idles at the logical high voltage. CPHA determines how data is outputted
> +and sampled.
> +
> +Note: LSB first indicates that data is transferred least significant bit first,and MSB first
> +indicates that data is transferred most significant bit first.
> +
> +\field{max_freq_hz} is the maximum clock rate supported in Hz unit, 0 means no limitation
> +for transfer speed.
> +
> +\field{max_word_delay_ns} is the maximum word delay supported in ns unit, 0 means word delay
> +feature is unsupported.
> +
> +Note: Just as one message contains a sequence of transfers, one transfer may contain
> +a sequence of words.
> +
> +\field{max_cs_setup_ns} is the maximum delay supported after chipselect is asserted, in ns unit,
> +0 means delay is not supported to introduce after chipselect is asserted.
> +
> +\field{max_cs_hold_ns} is the maximum delay supported before chipselect is deasserted, in ns unit,
> +0 means delay is not supported to introduce before chipselect is deasserted.
> +
> +\field{max_cs_incative_ns} is the maximum delay supported after chipselect is deasserted, in ns unit,
> +0 means delay is not supported to introduce after chipselect is deasserted.
> +
> +\subsection{Device Initialization}\label{sec:Device Types / SPI Controller Device / Device Initialization}
> +
> +\begin{enumerate}
> +\item The Virtio SPI driver configures and initializes the virtqueue.
> +\end{enumerate}
> +
> +\subsection{Device Operation}\label{sec:Device Types / SPI Controller Device / Device Operation}
> +
> +\subsubsection{Device Operation: Request Queue}\label{sec:Device Types / SPI Controller Device / Device Operation: Request Queue}
> +
> +The Virtio SPI driver enqueues requests to the virtqueue, and they are used by Virtio SPI device.
> +Each request represents one SPI transfer and is of the form:
> +
> +\begin{lstlisting}
> +struct virtio_spi_transfer_head {
> + u8 chip_select_id;
> + u8 bits_per_word;
> + u8 cs_change;
> + u8 tx_nbits;
> + u8 rx_nbits;
> + u8 reserved[3];
> + le32 mode;
> + le32 freq;
> + le32 word_delay_ns;
> + le32 cs_setup_ns;
> + le32 cs_delay_hold_ns;
> + le32 cs_change_delay_inactive_ns;
> +};
> +\end{lstlisting}
> +
> +\begin{lstlisting}
> +struct virtio_spi_transfer_result {
> + u8 result;
> +};
> +\end{lstlisting}
> +
> +\begin{lstlisting}
> +struct virtio_spi_transfer_req {
> + struct virtio_spi_transfer_head head;
> + u8 tx_buf[];
> + u8 rx_buf[];
> + struct virtio_spi_transfer_result result;
> +};
> +\end{lstlisting}
> +
> +\field{chip_select_id} indicates the chipselect index the SPI transfer used.
\field{chip_select_id} indicates the chipselect index to use for the SPI transfer.
> +\field{bits_per_word} indicates the number of bits in each SPI transfer word.
> +
> +\field{cs_change} indicates whether to deselect device before starting the next SPI transfer,
> +0 means chipselect keep asserted and 1 means chipselect deasserted then asserted again.
> +
> +\field{tx_nbits} indicates number of bits used for writing:
> + 0,1: SINGLE;
> + 2 : DUAL;
> + 4 : QUAD;
> + 8 : OCTAL;
> + other values are invalid.
> +
> +\field{rx_nbits} indicates number of bits used for reading:
> + 0,1: SINGLE;
> + 2 : DUAL;
> + 4 : QUAD;
> + 8 : OCTAL;
> + other values are invalid.
Duplication here can be removed too, like in the earlier example I gave.
Looks much better now. Thanks.
--
viresh
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