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spi: bcm2835: Polish transfer of DMA prologue

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Commit 3bd7f6589f ("spi: bcm2835: Overcome sglist entry length
limitation") was unfortunately merged even though submission of a
refined version was imminent.  Apply those refinements as an amendment:

* Drop no longer needed #include <asm/page.h>.  The lines requiring
  its inclusion were removed by the commit.

* Change type of tx_spillover flag from bool to unsigned int for
  consistency with dma_pending flag and pursuant to Linus' dictum:
  https://lkml.org/lkml/2017/11/21/384

* In bcm2835_rd_fifo_count() do not check for bs->rx_buf != NULL.
  The function will never be called if that's the case.

* Amend kerneldoc of bcm2835_wait_tx_fifo_empty() to prevent its use in
  situations where the function might spin forever.  (In response to a
  review comment by Stefan Wahren.)

* Sync only the cacheline containing the RX prologue back to memory,
  not the full first sglist entry.

* Use sg_dma_address() and sg_dma_len() instead of referencing the
  sglist entry members directly.  Seems to be the more common syntax in
  the tree, even for lvalues.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Frank Pavlic <f.pavlic@kunbus.de>
Cc: Martin Sperl <kernel@martin.sperl.org>
Cc: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Lukas Wunner 2018-11-29 16:45:24 +01:00 committed by Mark Brown
parent b12a084c87
commit b31a9299bc
No known key found for this signature in database
GPG Key ID: 24D68B725D5487D0
1 changed files with 29 additions and 25 deletions
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54
drivers/spi/spi-bcm2835.c
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@ -20,7 +20,6 @@
* GNU General Public License for more details.
*/
#include <asm/page.h>
#include <linux/clk.h>
#include <linux/completion.h>
#include <linux/delay.h>
@ -108,7 +107,7 @@ struct bcm2835_spi {
int rx_len;
int tx_prologue;
int rx_prologue;
bool tx_spillover;
unsigned int tx_spillover;
unsigned int dma_pending;
};
@ -155,21 +154,20 @@ static inline void bcm2835_wr_fifo(struct bcm2835_spi *bs)
* The caller must ensure that @bs->rx_len is greater than or equal to @count,
* that the RX FIFO contains at least @count bytes and that the DMA Enable flag
* in the CS register is set (such that a read from the FIFO register receives
* 32-bit instead of just 8-bit).
* 32-bit instead of just 8-bit). Moreover @bs->rx_buf must not be %NULL.
*/
static inline void bcm2835_rd_fifo_count(struct bcm2835_spi *bs, int count)
{
u32 val;
int len;
bs->rx_len -= count;
while (count > 0) {
val = bcm2835_rd(bs, BCM2835_SPI_FIFO);
if (bs->rx_buf) {
int len = min(count, 4);
memcpy(bs->rx_buf, &val, len);
bs->rx_buf += len;
}
len = min(count, 4);
memcpy(bs->rx_buf, &val, len);
bs->rx_buf += len;
count -= 4;
}
}
@ -187,12 +185,13 @@ static inline void bcm2835_rd_fifo_count(struct bcm2835_spi *bs, int count)
static inline void bcm2835_wr_fifo_count(struct bcm2835_spi *bs, int count)
{
u32 val;
int len;
bs->tx_len -= count;
while (count > 0) {
if (bs->tx_buf) {
int len = min(count, 4);
len = min(count, 4);
memcpy(&val, bs->tx_buf, len);
bs->tx_buf += len;
} else {
@ -206,6 +205,10 @@ static inline void bcm2835_wr_fifo_count(struct bcm2835_spi *bs, int count)
/**
* bcm2835_wait_tx_fifo_empty() - busy-wait for TX FIFO to empty
* @bs: BCM2835 SPI controller
*
* The caller must ensure that the RX FIFO can accommodate as many bytes
* as have been written to the TX FIFO: Transmission is halted once the
* RX FIFO is full, causing this function to spin forever.
*/
static inline void bcm2835_wait_tx_fifo_empty(struct bcm2835_spi *bs)
{
@ -379,11 +382,12 @@ static void bcm2835_spi_transfer_prologue(struct spi_master *master,
bcm2835_rd_fifo_count(bs, bs->rx_prologue);
bcm2835_spi_reset_hw(master);
dma_sync_sg_for_device(master->dma_rx->device->dev,
tfr->rx_sg.sgl, 1, DMA_FROM_DEVICE);
dma_sync_single_for_device(master->dma_rx->device->dev,
sg_dma_address(&tfr->rx_sg.sgl[0]),
bs->rx_prologue, DMA_FROM_DEVICE);
tfr->rx_sg.sgl[0].dma_address += bs->rx_prologue;
tfr->rx_sg.sgl[0].length -= bs->rx_prologue;
sg_dma_address(&tfr->rx_sg.sgl[0]) += bs->rx_prologue;
sg_dma_len(&tfr->rx_sg.sgl[0]) -= bs->rx_prologue;
}
/*
@ -401,12 +405,12 @@ static void bcm2835_spi_transfer_prologue(struct spi_master *master,
}
if (likely(!bs->tx_spillover)) {
tfr->tx_sg.sgl[0].dma_address += bs->tx_prologue;
tfr->tx_sg.sgl[0].length -= bs->tx_prologue;
sg_dma_address(&tfr->tx_sg.sgl[0]) += bs->tx_prologue;
sg_dma_len(&tfr->tx_sg.sgl[0]) -= bs->tx_prologue;
} else {
tfr->tx_sg.sgl[0].length = 0;
tfr->tx_sg.sgl[1].dma_address += 4;
tfr->tx_sg.sgl[1].length -= 4;
sg_dma_len(&tfr->tx_sg.sgl[0]) = 0;
sg_dma_address(&tfr->tx_sg.sgl[1]) += 4;
sg_dma_len(&tfr->tx_sg.sgl[1]) -= 4;
}
}
@ -426,17 +430,17 @@ static void bcm2835_spi_undo_prologue(struct bcm2835_spi *bs)
return;
if (bs->rx_prologue) {
tfr->rx_sg.sgl[0].dma_address -= bs->rx_prologue;
tfr->rx_sg.sgl[0].length += bs->rx_prologue;
sg_dma_address(&tfr->rx_sg.sgl[0]) -= bs->rx_prologue;
sg_dma_len(&tfr->rx_sg.sgl[0]) += bs->rx_prologue;
}
if (likely(!bs->tx_spillover)) {
tfr->tx_sg.sgl[0].dma_address -= bs->tx_prologue;
tfr->tx_sg.sgl[0].length += bs->tx_prologue;
sg_dma_address(&tfr->tx_sg.sgl[0]) -= bs->tx_prologue;
sg_dma_len(&tfr->tx_sg.sgl[0]) += bs->tx_prologue;
} else {
tfr->tx_sg.sgl[0].length = bs->tx_prologue - 4;
tfr->tx_sg.sgl[1].dma_address -= 4;
tfr->tx_sg.sgl[1].length += 4;
sg_dma_len(&tfr->tx_sg.sgl[0]) = bs->tx_prologue - 4;
sg_dma_address(&tfr->tx_sg.sgl[1]) -= 4;
sg_dma_len(&tfr->tx_sg.sgl[1]) += 4;
}
}