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 <[email protected]> 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 <[email protected]>
>> ---
>>   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 logical
> 
> s/clock idles/the clock idles/
> 
>> +low voltage, otherwise idles at the logical high voltage. CPHA determines how data is outputted
> 
> s/idles/it idles/
> 
Okay.

>> +and sampled.
>> +
>> +Note: LSB first indicates that data is transferred least significant bit first,and MSB first
> 
> missing 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 the
> 
> s/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 all
> 
> s/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 to
> 
> s/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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