Re: [PATCH v2 2/5] spi: move splitting transfers to spi_optimize_message()

[Nuno Sá]

On Mon, 2024-02-19 at 16:33 -0600, David Lechner wrote:
> Splitting transfers is an expensive operation so we can potentially
> optimize it by doing it only once per optimization of the message
> instead of repeating each time the message is transferred.
> 
> The transfer splitting functions are currently the only user of
> spi_res_alloc() so spi_res_release() can be safely moved at this time
> from spi_finalize_current_message() to spi_unoptimize_message().
> 
> The doc comments of the public functions for splitting transfers are
> also updated so that callers will know when it is safe to call them
> to ensure proper resource management.
> 
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> Signed-off-by: David Lechner <dlechner@xxxxxxxxxxxx>
> ---

Acked-by: Nuno Sa <nuno.sa@xxxxxxxxxx>

> 
> v2 changes:
> - Changed line break for multiline if condition
> - Removed kernel doc inclusion (/** -> /*) from static members
> - Picked up Jonathan's Reviewed-by
> 
>  drivers/spi/spi.c | 110 +++++++++++++++++++++++++++++++++---------------------
>  1 file changed, 68 insertions(+), 42 deletions(-)
> 
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index f68d92b57543..ba4d3fde2054 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -1747,38 +1747,6 @@ static int __spi_pump_transfer_message(struct spi_controller
> *ctlr,
>  
>  	trace_spi_message_start(msg);
>  
> -	/*
> -	 * If an SPI controller does not support toggling the CS line on each
> -	 * transfer (indicated by the SPI_CS_WORD flag) or we are using a GPIO
> -	 * for the CS line, we can emulate the CS-per-word hardware function by
> -	 * splitting transfers into one-word transfers and ensuring that
> -	 * cs_change is set for each transfer.
> -	 */
> -	if ((msg->spi->mode & SPI_CS_WORD) && (!(ctlr->mode_bits & SPI_CS_WORD) ||
> -					       spi_is_csgpiod(msg->spi))) {
> -		ret = spi_split_transfers_maxwords(ctlr, msg, 1);
> -		if (ret) {
> -			msg->status = ret;
> -			spi_finalize_current_message(ctlr);
> -			return ret;
> -		}
> -
> -		list_for_each_entry(xfer, &msg->transfers, transfer_list) {
> -			/* Don't change cs_change on the last entry in the list */
> -			if (list_is_last(&xfer->transfer_list, &msg->transfers))
> -				break;
> -			xfer->cs_change = 1;
> -		}
> -	} else {
> -		ret = spi_split_transfers_maxsize(ctlr, msg,
> -						  spi_max_transfer_size(msg-
> >spi));
> -		if (ret) {
> -			msg->status = ret;
> -			spi_finalize_current_message(ctlr);
> -			return ret;
> -		}
> -	}
> -
>  	if (ctlr->prepare_message) {
>  		ret = ctlr->prepare_message(ctlr, msg);
>  		if (ret) {
> @@ -2124,6 +2092,8 @@ static void __spi_unoptimize_message(struct spi_message *msg)
>  	if (ctlr->unoptimize_message)
>  		ctlr->unoptimize_message(msg);
>  
> +	spi_res_release(ctlr, msg);
> +
>  	msg->optimized = false;
>  	msg->opt_state = NULL;
>  }
> @@ -2169,15 +2139,6 @@ void spi_finalize_current_message(struct spi_controller
> *ctlr)
>  
>  	spi_unmap_msg(ctlr, mesg);
>  
> -	/*
> -	 * In the prepare_messages callback the SPI bus has the opportunity
> -	 * to split a transfer to smaller chunks.
> -	 *
> -	 * Release the split transfers here since spi_map_msg() is done on
> -	 * the split transfers.
> -	 */
> -	spi_res_release(ctlr, mesg);
> -
>  	if (mesg->prepared && ctlr->unprepare_message) {
>  		ret = ctlr->unprepare_message(ctlr, mesg);
>  		if (ret) {
> @@ -3819,6 +3780,10 @@ static int __spi_split_transfer_maxsize(struct
> spi_controller *ctlr,
>   * @msg:   the @spi_message to transform
>   * @maxsize:  the maximum when to apply this
>   *
> + * This function allocates resources that are automatically freed during the
> + * spi message unoptimize phase so this function should only be called from
> + * optimize_message callbacks.
> + *
>   * Return: status of transformation
>   */
>  int spi_split_transfers_maxsize(struct spi_controller *ctlr,
> @@ -3857,6 +3822,10 @@ EXPORT_SYMBOL_GPL(spi_split_transfers_maxsize);
>   * @msg:      the @spi_message to transform
>   * @maxwords: the number of words to limit each transfer to
>   *
> + * This function allocates resources that are automatically freed during the
> + * spi message unoptimize phase so this function should only be called from
> + * optimize_message callbacks.
> + *
>   * Return: status of transformation
>   */
>  int spi_split_transfers_maxwords(struct spi_controller *ctlr,
> @@ -4231,6 +4200,57 @@ static int __spi_validate(struct spi_device *spi, struct
> spi_message *message)
>  	return 0;
>  }
>  
> +/*
> + * spi_split_transfers - generic handling of transfer splitting
> + * @msg: the message to split
> + *
> + * Under certain conditions, a SPI controller may not support arbitrary
> + * transfer sizes or other features required by a peripheral. This function
> + * will split the transfers in the message into smaller transfers that are
> + * supported by the controller.
> + *
> + * Controllers with special requirements not covered here can also split
> + * transfers in the optimize_message() callback.
> + *
> + * Context: can sleep
> + * Return: zero on success, else a negative error code
> + */
> +static int spi_split_transfers(struct spi_message *msg)
> +{
> +	struct spi_controller *ctlr = msg->spi->controller;
> +	struct spi_transfer *xfer;
> +	int ret;
> +
> +	/*
> +	 * If an SPI controller does not support toggling the CS line on each
> +	 * transfer (indicated by the SPI_CS_WORD flag) or we are using a GPIO
> +	 * for the CS line, we can emulate the CS-per-word hardware function by
> +	 * splitting transfers into one-word transfers and ensuring that
> +	 * cs_change is set for each transfer.
> +	 */
> +	if ((msg->spi->mode & SPI_CS_WORD) &&
> +	    (!(ctlr->mode_bits & SPI_CS_WORD) || spi_is_csgpiod(msg->spi))) {
> +		ret = spi_split_transfers_maxwords(ctlr, msg, 1);
> +		if (ret)
> +			return ret;
> +
> +		list_for_each_entry(xfer, &msg->transfers, transfer_list) {
> +			/* Don't change cs_change on the last entry in the list */
> +			if (list_is_last(&xfer->transfer_list, &msg->transfers))
> +				break;
> +
> +			xfer->cs_change = 1;
> +		}
> +	} else {
> +		ret = spi_split_transfers_maxsize(ctlr, msg,
> +						  spi_max_transfer_size(msg-
> >spi));
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
>  /*
>   * __spi_optimize_message - shared implementation for spi_optimize_message()
>   *                          and spi_maybe_optimize_message()
> @@ -4254,10 +4274,16 @@ static int __spi_optimize_message(struct spi_device *spi,
>  	if (ret)
>  		return ret;
>  
> +	ret = spi_split_transfers(msg);
> +	if (ret)
> +		return ret;
> +
>  	if (ctlr->optimize_message) {
>  		ret = ctlr->optimize_message(msg);
> -		if (ret)
> +		if (ret) {
> +			spi_res_release(ctlr, msg);
>  			return ret;
> +		}
>  	}
>  
>  	msg->optimized = true;
>