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Subject: Re: [virtio-dev] [PATCH V6 2/2] virtio-spi: add the device specification
Hi Huck, On 11/30/2023 7:38 PM, Cornelia Huck wrote:
On Thu, Nov 30 2023, Haixu Cui <quic_haixcui@quicinc.com> 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, +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.I think it would still make sense to keep the host/guest example you included in the last version; while we have to talk about device/driver in the specification, giving host/guest as an example is completely fine.
Okay, I will add it back to illustrate the host&guest scenario.
+ +\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/for Virtio SPI driver/for the driver/
Okay.
(matches what is said for other device types)+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.I wonder whether another term is now more commonly used... the Wikipedia article uses main/sub, is there a term that is usually used together with "controller"?
In Wikipedia,"Historically, this arrangement has been called master/slave. But to avoid referencing slavery, alternative names discussed in  Alternative namings have been used."
I am not quite sure if main/sub is widely used, but in latest Linux, still use master/slave but master is gradually replaced by "controller".
So I think "controller" here does make sense. What is your suggestion?
+ +\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; + 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. + +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. + +\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.s/no limitation/there is no limitation/
Okay.
+ +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 logicals/clock idles/the clock idles/+low voltage, otherwise idles at the logical high voltage. CPHA determines how data is outputteds/idles/it idles/
Okay.
+and sampled. + +Note: LSB first indicates that data is transferred least significant bit first,and MSB firstmissing space after the comma
Okay.
+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{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. + +\field{reserved} is currently unused and might be used for further extensions in the future. + +\field{mode} indicates some transfer settings. Bit definitions as follows: + bit 0: CPHA, determines the timing (i.e. phase) of the data bits relative to the + clock pulses. + bit 1: CPOL, determines the polarity of the clock. + bit 2: CS_HIGH, if 1, chipselect active high, else active low. + bit 3: LSB_FIRST, determines per-word bits-on-wire, if 0, MSB first, else LSB first. + bit 4: LOOP, if 1, device is in loopback mode, else normal mode. + +\field{freq} indicates the SPI transfer speed in Hz. + +\field{word_delay_ns} indicates delay to be inserted between consecutive words of a transfer, +in ns unit. + +\field{cs_setup_ns} indicates delay to be introduced after chipselect is asserted, in ns unit. + +\field{cs_delay_hold_ns} indicates delay to be introduced before chipselect is deasserted, +in ns unit. + +\field{cs_change_delay_inactive_ns} indicates delay to be introduced after chipselect is +deasserted and before next asserted, in ns unit. + +\field{tx_buf} is the buffer for data sent to the device. + +\field{rx_buf} is the buffer for data received from the device. + +\field{result} is the transfer result, it may be one of the following values: + +\begin{lstlisting} +#define VIRTIO_SPI_TRANS_OK 0 +#define VIRTIO_SPI_PARAM_ERR 1 +#define VIRTIO_SPI_TRANS_ERR 2 +\end{lstlisting} + +VIRTIO_SPI_TRANS_OK indicates successful completion of the transfer. + +VIRTIO_SPI_PARAM_ERR indicates a parameter error, which means the parameters in +\field{struct virtio_spi_transfer_head} are not all valid, or some fields are set as +non-zero values but the corresponding features are not supported by device. +Especially, for full-duplex transfer, VIRTIO_SPI_PARAM_ERR also used to indicate thes/Especially/In particular/+scenario that the buffer size of \field{tx_buf} is not equal to that of \field{rx_buf}.Maybe "VIRTIO_SPI_PARAM_ERR can also indicate that \field{tx_buf} and \field{rx_buf} are not of the same length." ?
Yes, looks much better, I will update the statement.
+ +VIRTIO_SPI_TRANS_ERR indicates a transfer error, means that the parameters are alls/means/which means/+valid but trasnfer process failed.s/trasnfer/the transfer/+ +\subsubsection{Device Operation: Operation Status}\label{sec:Device Types / SPI Controller Device / Device Operation: Operation Status} + +Fields in \field{struct virtio_spi_transfer_head} are written by Virtio SPI driver, while +\field{result} in \field{struct virtio_spi_transfer_result} is written by Virtio SPI device. + +virtio-spi supports three transfer types: +\begin{itemize} +\item half-duplex read; +\item half-duplex write; +\item full-duplex transfer. +\end{itemize} + +For half-duplex read and full-duplex transfer, \field{rx_buf} is filled by Virtio SPI device +and consumed by Virtio SPI driver. For half-duplex write and full-duplex transfer, \field{tx_buf} +is filled by Virtio SPI driver and consumed by Virtio SPI device. + +\drivernormative{\subsubsection}{Device Operation}{Device Types / SPI Controller Device / Device Operation} + +For half-duplex read, Virtio SPI driver MUST send \field{struct virtio_spi_transfer_head}, +\field{rx_buf} and \field{struct virtio_spi_transfer_result} to SPI Virtio Device in order.Maybe "in that order" instead of "in order" (also below)?
Sure, will use "in that order".
+ +For half-duplex write, Virtio SPI driver MUST send \field{struct virtio_spi_transfer_head}, +\field{tx_buf} and \field{struct virtio_spi_transfer_result} to SPI Virtio Device in order. + +For full-duplex transfer, Virtio SPI driver MUST send \field{struct virtio_spi_transfer_head}, +\field{tx_buf}, \field{rx_buf} and \field{struct virtio_spi_transfer_result} to SPI Virtio Device in order. + +For full-duplex transfer, Virtio SPI driver MUST guarantee that the buffer size of \field{tx_buf} +and \field{rx_buf} is the same. + +Virtio SPI driver MUST not use \field{rx_buf} if the \field{result} returned from Virtio SPI device is +not VIRTIO_SPI_TRANS_OK. + +\devicenormative{\subsubsection}{Device Operation}{Device Types / SPI Controller Device / Device Operation} + +Virtio SPI device MUST set all the fields of \field{struct virtio_spi_config} before they are +read by Virtio SPI driver. + +Virtio SPI device MUST NOT change the data in \field{tx_buf}. + +Virtio SPI device MUST verify the parameters in \field{struct virtio_spi_transfer_head} after receiving +the request, and MUST set \field{struct virtio_spi_transfer_result} as VIRTIO_SPI_PARAM_ERR if not all +parameters are valid or some device unsupported features are set. + +For full-duplex transfer, Virtio SPI device MUST verify if the buffer size of \field{tx_buf} is equal tos/if/that/
Okay.
+that of \field{rx_buf}. If not, Virtio SPI device MUST set \field{struct virtio_spi_transfer_result} +as VIRTIO_SPI_PARAM_ERR.
Thank you very much. Best Regards Haixu Cui
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