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authorMartin Sperl <kernel@martin.sperl.org>2015-03-23 15:11:53 +0100
committerpopcornmix <popcornmix@gmail.com>2015-05-18 14:12:22 +0100
commitec9ba6fa160bce5005881e7bda743892cb838fae (patch)
tree43abe3130647ccde7a57fbeaeeacc109c459a8de /drivers
parenta94e95c5634f9372354f938cf2f5b3f759bdafaf (diff)
downloadlinux-ec9ba6fa160bce5005881e7bda743892cb838fae.tar.gz
spi: bcm2835: fill/drain SPI-fifo as much as possible during interrupt
Implement the recommendation from the BCM2835 data-sheet with regards to polling drivers to fill/drain the FIFO as much data as possible also for the interrupt-driven case (which this driver is making use of). This means that for long transfers (>64bytes) we need one interrupt every 64 bytes instead of every 12 bytes, as the FIFO is 16 words (not bytes) wide. Tested with mcp251x (can bus), fb_st7735 (TFT framebuffer device) and enc28j60 (ethernet) drivers. Signed-off-by: Martin Sperl <kernel@martin.sperl.org> Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/spi/spi-bcm2835.c78
1 files changed, 17 insertions, 61 deletions
diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
index 779d3a86c3cb..960dcce607c2 100644
--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -91,25 +91,23 @@ static inline void bcm2835_wr(struct bcm2835_spi *bs, unsigned reg, u32 val)
writel(val, bs->regs + reg);
}
-static inline void bcm2835_rd_fifo(struct bcm2835_spi *bs, int len)
+static inline void bcm2835_rd_fifo(struct bcm2835_spi *bs)
{
u8 byte;
- while (len--) {
+ while (bcm2835_rd(bs, BCM2835_SPI_CS) & BCM2835_SPI_CS_RXD) {
byte = bcm2835_rd(bs, BCM2835_SPI_FIFO);
if (bs->rx_buf)
*bs->rx_buf++ = byte;
}
}
-static inline void bcm2835_wr_fifo(struct bcm2835_spi *bs, int len)
+static inline void bcm2835_wr_fifo(struct bcm2835_spi *bs)
{
u8 byte;
- if (len > bs->len)
- len = bs->len;
-
- while (len--) {
+ while ((bs->len) &&
+ (bcm2835_rd(bs, BCM2835_SPI_CS) & BCM2835_SPI_CS_TXD)) {
byte = bs->tx_buf ? *bs->tx_buf++ : 0;
bcm2835_wr(bs, BCM2835_SPI_FIFO, byte);
bs->len--;
@@ -122,60 +120,24 @@ static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id)
struct bcm2835_spi *bs = spi_master_get_devdata(master);
u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS);
- /*
- * RXR - RX needs Reading. This means 12 (or more) bytes have been
- * transmitted and hence 12 (or more) bytes have been received.
- *
- * The FIFO is 16-bytes deep. We check for this interrupt to keep the
- * FIFO full; we have a 4-byte-time buffer for IRQ latency. We check
- * this before DONE (TX empty) just in case we delayed processing this
- * interrupt for some reason.
- *
- * We only check for this case if we have more bytes to TX; at the end
- * of the transfer, we ignore this pipelining optimization, and let
- * bcm2835_spi_finish_transfer() drain the RX FIFO.
- */
- if (bs->len && (cs & BCM2835_SPI_CS_RXR)) {
- /* Read 12 bytes of data */
- bcm2835_rd_fifo(bs, 12);
+ /* Read as many bytes as possible from FIFO */
+ bcm2835_rd_fifo(bs);
- /* Write up to 12 bytes */
- bcm2835_wr_fifo(bs, 12);
+ if (bs->len) { /* there is more data to transmit */
+ bcm2835_wr_fifo(bs);
+ } else { /* Transfer complete */
+ /* Disable SPI interrupts */
+ cs &= ~(BCM2835_SPI_CS_INTR | BCM2835_SPI_CS_INTD);
+ bcm2835_wr(bs, BCM2835_SPI_CS, cs);
/*
- * We must have written something to the TX FIFO due to the
- * bs->len check above, so cannot be DONE. Hence, return
- * early. Note that DONE could also be set if we serviced an
- * RXR interrupt really late.
+ * Wake up bcm2835_spi_transfer_one(), which will call
+ * bcm2835_spi_finish_transfer(), to drain the RX FIFO.
*/
- return IRQ_HANDLED;
+ complete(&bs->done);
}
- /*
- * DONE - TX empty. This occurs when we first enable the transfer
- * since we do not pre-fill the TX FIFO. At any other time, given that
- * we refill the TX FIFO above based on RXR, and hence ignore DONE if
- * RXR is set, DONE really does mean end-of-transfer.
- */
- if (cs & BCM2835_SPI_CS_DONE) {
- if (bs->len) { /* First interrupt in a transfer */
- bcm2835_wr_fifo(bs, 16);
- } else { /* Transfer complete */
- /* Disable SPI interrupts */
- cs &= ~(BCM2835_SPI_CS_INTR | BCM2835_SPI_CS_INTD);
- bcm2835_wr(bs, BCM2835_SPI_CS, cs);
-
- /*
- * Wake up bcm2835_spi_transfer_one(), which will call
- * bcm2835_spi_finish_transfer(), to drain the RX FIFO.
- */
- complete(&bs->done);
- }
-
- return IRQ_HANDLED;
- }
-
- return IRQ_NONE;
+ return IRQ_HANDLED;
}
static int bcm2835_spi_start_transfer(struct spi_device *spi,
@@ -238,12 +200,6 @@ static int bcm2835_spi_finish_transfer(struct spi_device *spi,
struct bcm2835_spi *bs = spi_master_get_devdata(spi->master);
u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS);
- /* Drain RX FIFO */
- while (cs & BCM2835_SPI_CS_RXD) {
- bcm2835_rd_fifo(bs, 1);
- cs = bcm2835_rd(bs, BCM2835_SPI_CS);
- }
-
if (tfr->delay_usecs)
udelay(tfr->delay_usecs);