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Unverified Commit b31a9299 authored by Lukas Wunner's avatar Lukas Wunner Committed by Mark Brown
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spi: bcm2835: Polish transfer of DMA prologue 

Commit 3bd7f658 ("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: default avatarLukas 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: default avatarMark Brown <broonie@kernel.org>
parent b12a084c

drivers/spi/spi-bcm2835.c

+29 −25
Original line number Diff line number Diff line
@@ -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);

		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;

	}

}