Commit f1f640a9 authored by Vernon Sauder's avatar Vernon Sauder Committed by Linus Torvalds
Browse files

pxa2xx_spi: fix chip_info defaults and documentation. 



Make the chip info structure data optional by providing reasonable
defaults.  Improve corresponding documentation, and highlight the drawback
of not providing explicit chipselect control.

DMA can determine appropriate dma_burst_size and thresholds automatically
so use DMA even if dma_burst_size is not specified.

Signed-off-by: default avatarVernon Sauder <VernonInHand@gmail.com>
Reviewed-by: default avatarNed Forrester <nforrester@whoi.edu>
Signed-off-by: default avatarDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 65a00a20

Documentation/spi/pxa2xx

+23 −11
Original line number Diff line number Diff line
@@ -96,7 +96,7 @@ Each slave device attached to the PXA must provide slave specific configuration 
information via the structure "pxa2xx_spi_chip" found in

"arch/arm/mach-pxa/include/mach/pxa2xx_spi.h".  The pxa2xx_spi master controller driver

will uses the configuration whenever the driver communicates with the slave

device.

device. All fields are optional.



struct pxa2xx_spi_chip {

	u8 tx_threshold;
@@ -112,14 +112,17 @@ used to configure the SSP hardware fifo. These fields are critical to the 
performance of pxa2xx_spi driver and misconfiguration will result in rx

fifo overruns (especially in PIO mode transfers). Good default values are



	.tx_threshold = 12,

	.rx_threshold = 4,

	.tx_threshold = 8,

	.rx_threshold = 8,



The range is 1 to 16 where zero indicates "use default".



The "pxa2xx_spi_chip.dma_burst_size" field is used to configure PXA2xx DMA

engine and is related the "spi_device.bits_per_word" field.  Read and understand

the PXA2xx "Developer Manual" sections on the DMA controller and SSP Controllers

to determine the correct value. An SSP configured for byte-wide transfers would

use a value of 8.

use a value of 8. The driver will determine a reasonable default if

dma_burst_size == 0.



The "pxa2xx_spi_chip.timeout" fields is used to efficiently handle

trailing bytes in the SSP receiver fifo.  The correct value for this field is
@@ -137,7 +140,13 @@ function for asserting/deasserting a slave device chip select. If the field is 
NULL, the pxa2xx_spi master controller driver assumes that the SSP port is

configured to use SSPFRM instead.



NSSP SALVE SAMPLE

NOTE: the SPI driver cannot control the chip select if SSPFRM is used, so the

chipselect is dropped after each spi_transfer.  Most devices need chip select

asserted around the complete message.  Use SSPFRM as a GPIO (through cs_control)

to accomodate these chips.





NSSP SLAVE SAMPLE

-----------------

The pxa2xx_spi_chip structure is passed to the pxa2xx_spi driver in the

"spi_board_info.controller_data" field. Below is a sample configuration using
@@ -206,18 +215,21 @@ static void __init streetracer_init(void) 


DMA and PIO I/O Support

-----------------------

The pxa2xx_spi driver support both DMA and interrupt driven PIO message

transfers.  The driver defaults to PIO mode and DMA transfers must enabled by

setting the "enable_dma" flag in the "pxa2xx_spi_master" structure and

ensuring that the "pxa2xx_spi_chip.dma_burst_size" field is non-zero.  The DMA

mode support both coherent and stream based DMA mappings.

The pxa2xx_spi driver supports both DMA and interrupt driven PIO message

transfers.  The driver defaults to PIO mode and DMA transfers must be enabled

by setting the "enable_dma" flag in the "pxa2xx_spi_master" structure.  The DMA

mode supports both coherent and stream based DMA mappings.



The following logic is used to determine the type of I/O to be used on

a per "spi_transfer" basis:



if !enable_dma or dma_burst_size == 0 then

if !enable_dma then

	always use PIO transfers



if spi_message.len > 8191 then

	print "rate limited" warning

	use PIO transfers



if spi_message.is_dma_mapped and rx_dma_buf != 0 and tx_dma_buf != 0 then

	use coherent DMA mode

drivers/spi/pxa2xx_spi.c

+27 −19
Original line number Diff line number Diff line
@@ -47,6 +47,10 @@ MODULE_ALIAS("platform:pxa2xx-spi"); 


#define MAX_BUSES 3



#define RX_THRESH_DFLT 	8

#define TX_THRESH_DFLT 	8

#define TIMOUT_DFLT		1000



#define DMA_INT_MASK		(DCSR_ENDINTR | DCSR_STARTINTR | DCSR_BUSERR)

#define RESET_DMA_CHANNEL	(DCSR_NODESC | DMA_INT_MASK)

#define IS_DMA_ALIGNED(x)	((((u32)(x)) & 0x07) == 0)
@@ -1171,6 +1175,8 @@ static int setup(struct spi_device *spi) 
	struct driver_data *drv_data = spi_master_get_devdata(spi->master);

	struct ssp_device *ssp = drv_data->ssp;

	unsigned int clk_div;

	uint tx_thres = TX_THRESH_DFLT;

	uint rx_thres = RX_THRESH_DFLT;



	if (!spi->bits_per_word)

		spi->bits_per_word = 8;
@@ -1209,8 +1215,7 @@ static int setup(struct spi_device *spi) 


		chip->cs_control = null_cs_control;

		chip->enable_dma = 0;

		chip->timeout = 1000;

		chip->threshold = SSCR1_RxTresh(1) | SSCR1_TxTresh(1);

		chip->timeout = TIMOUT_DFLT;

		chip->dma_burst_size = drv_data->master_info->enable_dma ?

					DCMD_BURST8 : 0;

	}
@@ -1224,22 +1229,21 @@ static int setup(struct spi_device *spi) 
	if (chip_info) {

		if (chip_info->cs_control)

			chip->cs_control = chip_info->cs_control;



		if (chip_info->timeout)

			chip->timeout = chip_info->timeout;



		chip->threshold = (SSCR1_RxTresh(chip_info->rx_threshold) &

								SSCR1_RFT) |

				(SSCR1_TxTresh(chip_info->tx_threshold) &

								SSCR1_TFT);



		chip->enable_dma = chip_info->dma_burst_size != 0

					&& drv_data->master_info->enable_dma;

		if (chip_info->tx_threshold)

			tx_thres = chip_info->tx_threshold;

		if (chip_info->rx_threshold)

			rx_thres = chip_info->rx_threshold;

		chip->enable_dma = drv_data->master_info->enable_dma;

		chip->dma_threshold = 0;



		if (chip_info->enable_loopback)

			chip->cr1 = SSCR1_LBM;

	}



	chip->threshold = (SSCR1_RxTresh(rx_thres) & SSCR1_RFT) |

			(SSCR1_TxTresh(tx_thres) & SSCR1_TFT);



	/* set dma burst and threshold outside of chip_info path so that if

	 * chip_info goes away after setting chip->enable_dma, the

	 * burst and threshold can still respond to changes in bits_per_word */
@@ -1268,17 +1272,19 @@ static int setup(struct spi_device *spi) 


	/* NOTE:  PXA25x_SSP _could_ use external clocking ... */

	if (drv_data->ssp_type != PXA25x_SSP)

		dev_dbg(&spi->dev, "%d bits/word, %ld Hz, mode %d\n",

		dev_dbg(&spi->dev, "%d bits/word, %ld Hz, mode %d, %s\n",

				spi->bits_per_word,

				clk_get_rate(ssp->clk)

					/ (1 + ((chip->cr0 & SSCR0_SCR) >> 8)),

				spi->mode & 0x3);

				spi->mode & 0x3,

				chip->enable_dma ? "DMA" : "PIO");

	else

		dev_dbg(&spi->dev, "%d bits/word, %ld Hz, mode %d\n",

		dev_dbg(&spi->dev, "%d bits/word, %ld Hz, mode %d, %s\n",

				spi->bits_per_word,

				clk_get_rate(ssp->clk)

				clk_get_rate(ssp->clk) / 2

					/ (1 + ((chip->cr0 & SSCR0_SCR) >> 8)),

				spi->mode & 0x3);

				spi->mode & 0x3,

				chip->enable_dma ? "DMA" : "PIO");



	if (spi->bits_per_word <= 8) {

		chip->n_bytes = 1;
@@ -1498,7 +1504,9 @@ static int __init pxa2xx_spi_probe(struct platform_device *pdev) 


	/* Load default SSP configuration */

	write_SSCR0(0, drv_data->ioaddr);

	write_SSCR1(SSCR1_RxTresh(4) | SSCR1_TxTresh(12), drv_data->ioaddr);

	write_SSCR1(SSCR1_RxTresh(RX_THRESH_DFLT) |

				SSCR1_TxTresh(TX_THRESH_DFLT),

				drv_data->ioaddr);

	write_SSCR0(SSCR0_SerClkDiv(2)

			| SSCR0_Motorola

			| SSCR0_DataSize(8),

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