On Wed, Mar 19, 2014 at 04:28:57PM -0500, Alexandru Gagniuc wrote:
> SPI transfers were limited to one FIFO depth, which is 64 bytes.
> This was an artificial limitation, however, as the hardware can handle
> much larger bursts. To accommodate this, we enable the interrupt when
> the Rx FIFO is 3/4 full, and drain the FIFO within the interrupt
> handler. The 3/4 ratio was chosen arbitrarily, with the intention to
> reduce the potential number of interrupts.
>
> Since the SUN4I_CTL_TP bit is set, the hardware will pause
> transmission whenever the FIFO is full, so there is no risk of losing
> data if we can't service the interrupt in time.
>
> For the Tx side, enable and use the Tx FIFO 3/4 empty interrupt to
> replenish the FIFO on large SPI bursts. This requires more care in
> when the interrupt is left enabled, as this interrupt will continually
> trigger when the FIFO is less than 1/4 full, even though we
> acknowledge it.
>
> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@xxxxxxxxx>
> ---
> drivers/spi/spi-sun4i.c | 67 +++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 62 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
> index 3f82705..9dd55d3 100644
> --- a/drivers/spi/spi-sun4i.c
> +++ b/drivers/spi/spi-sun4i.c
> @@ -47,6 +47,8 @@
> #define SUN4I_CTL_TP BIT(18)
>
> #define SUN4I_INT_CTL_REG 0x0c
> +#define SUN4I_INT_CTL_RF_F34 BIT(4)
> +#define SUN4I_INT_CTL_TF_E34 BIT(12)
> #define SUN4I_INT_CTL_TC BIT(16)
>
> #define SUN4I_INT_STA_REG 0x10
> @@ -68,6 +70,8 @@
> #define SUN4I_XMIT_CNT_REG 0x24
> #define SUN4I_XMIT_CNT(cnt) ((cnt) & 0xffffff)
>
> +#define SUN4I_MAX_XFER_SIZE 0xffffff
> +
I'd rather define the mask only once here, and reuse it in the macro
just above.
> #define SUN4I_FIFO_STA_REG 0x28
> #define SUN4I_FIFO_STA_RF_CNT_MASK 0x7f
> #define SUN4I_FIFO_STA_RF_CNT_BITS 0
> @@ -97,6 +101,28 @@ static inline void sun4i_spi_write(struct sun4i_spi *sspi, u32 reg, u32 value)
> writel(value, sspi->base_addr + reg);
> }
>
> +static inline u32 sun4i_spi_get_tx_fifo_count(struct sun4i_spi *sspi)
> +{
> + u32 reg;
> + reg = sun4i_spi_read(sspi, SUN4I_FIFO_STA_REG);
> + reg >>= SUN4I_FIFO_STA_TF_CNT_BITS;
> + return reg & SUN4I_FIFO_STA_TF_CNT_MASK;
> +}
> +
> +static inline void sun4i_spi_enable_interrupt(struct sun4i_spi *sspi, u32 mask)
> +{
> + u32 reg = sun4i_spi_read(sspi, SUN4I_INT_CTL_REG);
> + reg |= mask;
> + sun4i_spi_write(sspi, SUN4I_INT_CTL_REG, reg);
> +}
> +
> +static inline void sun4i_spi_disable_interrupt(struct sun4i_spi *sspi, u32 mask)
> +{
> + u32 reg = sun4i_spi_read(sspi, SUN4I_INT_CTL_REG);
> + reg &= ~mask;
> + sun4i_spi_write(sspi, SUN4I_INT_CTL_REG, reg);
> +}
> +
> static inline void sun4i_spi_drain_fifo(struct sun4i_spi *sspi, int len)
> {
> u32 reg, cnt;
> @@ -119,8 +145,15 @@ static inline void sun4i_spi_drain_fifo(struct sun4i_spi *sspi, int len)
>
> static inline void sun4i_spi_fill_fifo(struct sun4i_spi *sspi, int len)
> {
> + u32 cnt;
> u8 byte;
>
> + /* See how much data we can fit */
> + cnt = SUN4I_FIFO_DEPTH - sun4i_spi_get_tx_fifo_count(sspi);
> +
> + if (len > cnt)
> + len = cnt;
> +
> if (len > sspi->len)
> len = sspi->len;
>
> @@ -175,8 +208,7 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
> int ret = 0;
> u32 reg;
>
> - /* We don't support transfer larger than the FIFO */
> - if (tfr->len > SUN4I_FIFO_DEPTH)
> + if (tfr->len > SUN4I_MAX_XFER_SIZE)
A comment here about why you're doing so would be nice
> return -EINVAL;
>
> reinit_completion(&sspi->done);
> @@ -274,7 +306,11 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
> sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
>
> /* Enable the interrupts */
> - sun4i_spi_write(sspi, SUN4I_INT_CTL_REG, SUN4I_INT_CTL_TC);
> + reg = SUN4I_INT_CTL_TC | SUN4I_INT_CTL_RF_F34;
> + /* Only enable Tx FIFO interrupt if we really need it */
> + if (tx_len > SUN4I_FIFO_DEPTH)
> + reg |= SUN4I_INT_CTL_TF_E34;
> + sun4i_spi_write(sspi, SUN4I_INT_CTL_REG, reg);
You probably can use the _enable_interrupt function you just defined here :)
>
> /* Start the transfer */
> reg = sun4i_spi_read(sspi, SUN4I_CTL_REG);
> @@ -287,8 +323,6 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
> goto out;
> }
>
> - sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
> -
> out:
> sun4i_spi_write(sspi, SUN4I_INT_CTL_REG, 0);
>
> @@ -303,10 +337,33 @@ static irqreturn_t sun4i_spi_handler(int irq, void *dev_id)
> /* Transfer complete */
> if (status & SUN4I_INT_CTL_TC) {
> sun4i_spi_write(sspi, SUN4I_INT_STA_REG, SUN4I_INT_CTL_TC);
> + sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
> complete(&sspi->done);
> return IRQ_HANDLED;
> }
>
> + /* Receive FIFO 3/4 full */
> + if (status & SUN4I_INT_CTL_RF_F34) {
> + sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
> + /* Only clear the interrupt _after_ draining the FIFO */
> + sun4i_spi_write(sspi, SUN4I_INT_STA_REG, SUN4I_INT_CTL_RF_F34);
> + return IRQ_HANDLED;
> + }
> +
> + /* Transmit FIFO 3/4 empty */
> + if (status & SUN4I_INT_CTL_TF_E34) {
> + sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
> +
> + if(!sspi->len)
> + /* nothing left to transmit */
> + sun4i_spi_disable_interrupt(sspi, SUN4I_INT_CTL_TF_E34);
> +
> + /* Only clear the interrupt _after_ re-seeding the FIFO */
> + sun4i_spi_write(sspi, SUN4I_INT_STA_REG, SUN4I_INT_CTL_TF_E34);
> +
> + return IRQ_HANDLED;
> + }
> +
> return IRQ_NONE;
> }
>
> --
> 1.8.5.3
>
--
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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