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authorVladimir Oltean <vladimir.oltean@nxp.com>2020-03-05 00:00:43 +0200
committerMark Brown <broonie@kernel.org>2020-03-05 14:06:23 +0000
commitea93ed4c181bd42d27b49b612d56f4ceb23d1d6c (patch)
treeb445fb955c8d65536eb17bd55471ef11fcdc1bbc /drivers/spi
parent6365504d42d90c68555ee40cdf297a1f187cb4a3 (diff)
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spi: spi-fsl-dspi: Use EOQ for last word in buffer even for XSPI mode
The EOQ mode has a hardware limitation in that it stops the transmission (including the deassertion of the chip select signal) once the host CPU requests end-of-queue for a particular word in the TX FIFO. And XSPI mode has a limitation in that we need a separate CMD FIFO entry for the last byte in the buffer, where the chip select signal needs to be deasserted. It's not a functional limitation, but it's rather clunky and the fact that we need to halt the pipeline and write a single entry to the TX FIFO whenever a buffer ends brings the throughput down when transmitting small buffers. So the idea here is to use EOQ's limitation in our favor when using XSPI mode. Stop special-casing that final word in the buffer, and just kill the chip select signal by issuing an EOQ for that last word. Now it can be mixed in with all the other words in the current TX FIFO train. A small trick here is that we still keep using the XSPI-specific signaling via the CMDTCFQ interrupt in RSER, and not enabling the EOQ interrupt, in order to avoid hardware weirdness (potential races with separate interrupts being raised for CMDTCFQ and EOQ for what is in fact the end of the same transmission). That is just theoretical, but it's good to be cautious, and the EOQ interrupt isn't needed. Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Link: https://lore.kernel.org/r/20200304220044.11193-12-olteanv@gmail.com Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'drivers/spi')
-rw-r--r--drivers/spi/spi-fsl-dspi.c22
1 files changed, 13 insertions, 9 deletions
diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
index df4944353ed5..d5983be32180 100644
--- a/drivers/spi/spi-fsl-dspi.c
+++ b/drivers/spi/spi-fsl-dspi.c
@@ -656,10 +656,8 @@ static void dspi_pushr_write(struct fsl_dspi *dspi)
regmap_write(dspi->regmap, SPI_PUSHR, dspi_pop_tx_pushr(dspi));
}
-static void dspi_pushr_cmd_write(struct fsl_dspi *dspi)
+static void dspi_pushr_cmd_write(struct fsl_dspi *dspi, u16 cmd)
{
- u16 cmd = dspi->tx_cmd;
-
/*
* The only time when the PCS doesn't need continuation after this word
* is when it's last. We need to look ahead, because we actually call
@@ -680,8 +678,13 @@ static void dspi_pushr_txdata_write(struct fsl_dspi *dspi, u16 txdata)
regmap_write(dspi->regmap_pushr, PUSHR_TX, txdata);
}
-static void dspi_xspi_write(struct fsl_dspi *dspi, int cnt)
+static void dspi_xspi_write(struct fsl_dspi *dspi, int cnt, bool eoq)
{
+ u16 tx_cmd = dspi->tx_cmd;
+
+ if (eoq)
+ tx_cmd |= SPI_PUSHR_CMD_EOQ;
+
/* Update CTARE */
regmap_write(dspi->regmap, SPI_CTARE(0),
SPI_FRAME_EBITS(dspi->oper_bits_per_word) |
@@ -691,7 +694,7 @@ static void dspi_xspi_write(struct fsl_dspi *dspi, int cnt)
* Write the CMD FIFO entry first, and then the two
* corresponding TX FIFO entries (or one...).
*/
- dspi_pushr_cmd_write(dspi);
+ dspi_pushr_cmd_write(dspi, tx_cmd);
/* Fill TX FIFO with as many transfers as possible */
while (cnt--) {
@@ -707,6 +710,7 @@ static void dspi_xspi_fifo_write(struct fsl_dspi *dspi)
{
int num_fifo_entries = dspi->devtype_data->fifo_size;
int bytes_in_flight;
+ bool eoq = false;
/* In XSPI mode each 32-bit word occupies 2 TX FIFO entries */
if (dspi->oper_word_size == 4)
@@ -732,11 +736,11 @@ static void dspi_xspi_fifo_write(struct fsl_dspi *dspi)
* So send one word less during this go, to force a split and a command
* with a single word next time, when CONT will be unset.
*/
- if (bytes_in_flight == dspi->len && dspi->words_in_flight > 1 &&
- !(dspi->tx_cmd & SPI_PUSHR_CMD_CONT))
- dspi->words_in_flight--;
+ if (!(dspi->tx_cmd & SPI_PUSHR_CMD_CONT) &&
+ bytes_in_flight == dspi->len)
+ eoq = true;
- dspi_xspi_write(dspi, dspi->words_in_flight);
+ dspi_xspi_write(dspi, dspi->words_in_flight, eoq);
}
static void dspi_eoq_fifo_write(struct fsl_dspi *dspi)