Dear Trent Piepho,
> There are three flag arguments to the PIO and DMA txrx functions. Two
> are passed as pointers to integers, even though they are input only
> and not modified, which makes no sense to do. The third is passed as
> an integer.
>
> The compiler must use an argument register or stack variable for each
> flag this way. By using bitflags in a single flag argument more
> efficient and smaller code is produced since all the flags can fit in
> a single register. And all the flag arguments get cumbersome,
> especially when more are added for things like GPIO chipselects.
>
> The "first" flag is never used, so can just be deleted.
>
> The "last" flag is renamed to DEASSERT_CS, since that's really what it
> does. The spi_transfer cs_change flag means that CS might be
> de-asserted on a transfer which is not last and not de-assert on the
> last transfer, so it is not which transfer is the last we need to know
> but rather the transfers which after which CS should be de-asserted.
>
> This also extends the driver to not ignore cs_change when setting the
> DEASSERT_CS nee "last" flag.
>
> Signed-off-by: Trent Piepho <tpie...@gmail.com>
> Cc: Marek Vasut <ma...@denx.de>
> Cc: Fabio Estevam <fabio.este...@freescale.com>
> Cc: Shawn Guo <shawn....@linaro.org>
> ---
> drivers/spi/spi-mxs.c | 55
> ++++++++++++++++++++++++++++--------------------- 1 file changed, 31
> insertions(+), 24 deletions(-)
>
> diff --git a/drivers/spi/spi-mxs.c b/drivers/spi/spi-mxs.c
> index 7eb4bc9..3064304 100644
> --- a/drivers/spi/spi-mxs.c
> +++ b/drivers/spi/spi-mxs.c
> @@ -58,6 +58,13 @@
>
> #define SG_MAXLEN 0xff00
>
> +/*
> + * Flags for txrx functions. More efficient that using an argument
> register for + * each one.
> + */
> +#define TXRX_WRITE 1 /* This is a write */
> +#define TXRX_DEASSERT_CS 2 /* De-assert CS at end of txrx */
> +
Use (1 << n) here as these are bitfield flags.
[...]
> @@ -409,10 +418,9 @@ static int mxs_spi_transfer_one(struct spi_master
> *master, if (status)
> break;
>
> - if (&t->transfer_list == m->transfers.next)
> - first = 1;
> - if (&t->transfer_list == m->transfers.prev)
> - last = 1;
> + /* De-assert on last transfer, inverted by cs_change flag */
> + flag = (&t->transfer_list == m->transfers.prev) ^ t->cs_change ?
> + TXRX_DEASSERT_CS : 0;
Make this into an if-else block, this really is hard to parse at first glance.
> if ((t->rx_buf && t->tx_buf) || (t->rx_dma && t->tx_dma)) {
> dev_err(ssp->dev,
> "Cannot send and receive simultaneously\n");
[...]
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