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;
>
