Re: [PATCH 3/3] i2c: at91: add support to FIFOs

From: Ludovic Desroches
Date: Mon Jun 01 2015 - 05:44:09 EST

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Hi Cyrille,

Some comments otherwise

Acked-by: Ludovic Desroches <ludovic.desroches@xxxxxxxxx>

On Fri, May 29, 2015 at 03:50:10PM +0200, Cyrille Pitchen wrote:
> When FIFOs are available and enabled, the driver now configures the Atmel
> eXtended DMA Controller to perform word accesses instead of byte accesses
> when possible.
> The actual access width depends on the size of the buffer to transmit.
>
> To enable FIFO support the "atmel,fifo-size" property must be set properly
> in the I2C controller node of the device tree.
>

Maybe we should describe this parameter in the device tree binding
documentation.

> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@xxxxxxxxx>
> ---
> drivers/i2c/busses/i2c-at91.c | 146 +++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 129 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
> index 1549b29..c061c19 100644
> --- a/drivers/i2c/busses/i2c-at91.c
> +++ b/drivers/i2c/busses/i2c-at91.c
> @@ -54,6 +54,8 @@
> #define AT91_TWI_THRCLR (1 << 24) /* Transmit Holding Register Clear */
> #define AT91_TWI_RHRCLR (1 << 25) /* Receive Holding Register Clear */
> #define AT91_TWI_LOCKCLR (1 << 26) /* Lock Clear */
> +#define AT91_TWI_FIFOEN (1 << 28) /* FIFO Enable */
> +#define AT91_TWI_FIFODIS (1 << 29) /* FIFO Disable */
>

Use BIT() macro. Cleanup should be done in another patch, see comments
for patch 1/3.

> #define AT91_TWI_MMR 0x0004 /* Master Mode Register */
> #define AT91_TWI_IADRSZ_1 0x0100 /* Internal Device Address Size */
> @@ -85,6 +87,22 @@
> #define AT91_TWI_ACR_DATAL(len) ((len) & 0xff)
> #define AT91_TWI_ACR_DIR (1 << 8)
>
> +#define AT91_TWI_FMR 0x0050 /* FIFO Mode Register */
> +#define AT91_TWI_FMR_TXRDYM(mode) (((mode) & 0x3) << 0)
> +#define AT91_TWI_FMR_TXRDYM_MASK (0x3 << 0)
> +#define AT91_TWI_FMR_RXRDYM(mode) (((mode) & 0x3) << 4)
> +#define AT91_TWI_FMR_RXRDYM_MASK (0x3 << 4)
> +#define AT91_TWI_ONE_DATA 0x0
> +#define AT91_TWI_TWO_DATA 0x1
> +#define AT91_TWI_FOUR_DATA 0x2
> +
> +#define AT91_TWI_FLR 0x0054 /* FIFO Level Register */
> +
> +#define AT91_TWI_FSR 0x0060 /* FIFO Status Register */
> +#define AT91_TWI_FIER 0x0064 /* FIFO Interrupt Enable Register */
> +#define AT91_TWI_FIDR 0x0068 /* FIFO Interrupt Disable Register */
> +#define AT91_TWI_FIMR 0x006c /* FIFO Interrupt Mask Register */
> +
> #define AT91_TWI_VER 0x00fc /* Version Register */
>
> struct at91_twi_pdata {
> @@ -98,7 +116,7 @@ struct at91_twi_pdata {
> struct at91_twi_dma {
> struct dma_chan *chan_rx;
> struct dma_chan *chan_tx;
> - struct scatterlist sg;
> + struct scatterlist sg[2];
> struct dma_async_tx_descriptor *data_desc;
> enum dma_data_direction direction;
> bool buf_mapped;
> @@ -121,6 +139,7 @@ struct at91_twi_dev {
> struct at91_twi_pdata *pdata;
> bool use_dma;
> bool recv_len_abort;
> + u32 fifo_size;
> struct at91_twi_dma dma;
> };
>
> @@ -154,6 +173,9 @@ static void at91_init_twi_bus(struct at91_twi_dev *dev)
> {
> at91_disable_twi_interrupts(dev);
> at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_SWRST);
> + /* FIFO should be enabled immediately after the software reset */
> + if (dev->fifo_size)
> + at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_FIFOEN);
> at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_MSEN);
> at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_SVDIS);
> at91_twi_write(dev, AT91_TWI_CWGR, dev->twi_cwgr_reg);
> @@ -200,7 +222,7 @@ static void at91_twi_dma_cleanup(struct at91_twi_dev *dev)
> dma->xfer_in_progress = false;
> }
> if (dma->buf_mapped) {
> - dma_unmap_single(dev->dev, sg_dma_address(&dma->sg),
> + dma_unmap_single(dev->dev, sg_dma_address(&dma->sg[0]),
> dev->buf_len, dma->direction);
> dma->buf_mapped = false;
> }
> @@ -213,7 +235,8 @@ static void at91_twi_write_next_byte(struct at91_twi_dev *dev)
> if (dev->buf_len <= 0)
> return;
>
> - at91_twi_write(dev, AT91_TWI_THR, *dev->buf);
> + /* 8bit write works with and without FIFO */
> + writeb_relaxed(*dev->buf, dev->base + AT91_TWI_THR);
>
> /* send stop when last byte has been written */
> if (--dev->buf_len == 0) {
> @@ -231,7 +254,7 @@ static void at91_twi_write_data_dma_callback(void *data)
> {
> struct at91_twi_dev *dev = (struct at91_twi_dev *)data;
>
> - dma_unmap_single(dev->dev, sg_dma_address(&dev->dma.sg),
> + dma_unmap_single(dev->dev, sg_dma_address(&dev->dma.sg[0]),
> dev->buf_len, DMA_TO_DEVICE);
>
> /*
> @@ -252,6 +275,7 @@ static void at91_twi_write_data_dma(struct at91_twi_dev *dev)
> struct dma_async_tx_descriptor *txdesc;
> struct at91_twi_dma *dma = &dev->dma;
> struct dma_chan *chan_tx = dma->chan_tx;
> + unsigned int sg_len = 1;
>
> if (dev->buf_len <= 0)
> return;
> @@ -267,10 +291,43 @@ static void at91_twi_write_data_dma(struct at91_twi_dev *dev)
> }
> dma->buf_mapped = true;
> at91_twi_irq_restore(dev);
> - sg_dma_len(&dma->sg) = dev->buf_len;
> - sg_dma_address(&dma->sg) = dma_addr;
>
> - txdesc = dmaengine_prep_slave_sg(chan_tx, &dma->sg, 1, DMA_MEM_TO_DEV,
> + if (dev->fifo_size) {
> + size_t part1_len, part2_len;
> + struct scatterlist *sg;
> + unsigned fifo_mr;
> +
> + sg_len = 0;
> +
> + part1_len = dev->buf_len & ~0x3;
> + if (part1_len) {
> + sg = &dma->sg[sg_len++];
> + sg_dma_len(sg) = part1_len;
> + sg_dma_address(sg) = dma_addr;
> + }
> +
> + part2_len = dev->buf_len & 0x3;
> + if (part2_len) {
> + sg = &dma->sg[sg_len++];
> + sg_dma_len(sg) = part2_len;
> + sg_dma_address(sg) = dma_addr + part1_len;
> + }
> +
> + /*
> + * DMA controller is triggered when at least 4 data can be
> + * written into the TX FIFO
> + */
> + fifo_mr = at91_twi_read(dev, AT91_TWI_FMR);
> + fifo_mr &= ~AT91_TWI_FMR_TXRDYM_MASK;
> + fifo_mr |= AT91_TWI_FMR_TXRDYM(AT91_TWI_FOUR_DATA);
> + at91_twi_write(dev, AT91_TWI_FMR, fifo_mr);
> + } else {
> + sg_dma_len(&dma->sg[0]) = dev->buf_len;
> + sg_dma_address(&dma->sg[0]) = dma_addr;
> + }
> +
> + txdesc = dmaengine_prep_slave_sg(chan_tx, dma->sg, sg_len,
> + DMA_MEM_TO_DEV,
> DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
> if (!txdesc) {
> dev_err(dev->dev, "dma prep slave sg failed\n");
> @@ -295,7 +352,8 @@ static void at91_twi_read_next_byte(struct at91_twi_dev *dev)
> if (dev->buf_len <= 0)
> return;
>
> - *dev->buf = at91_twi_read(dev, AT91_TWI_RHR) & 0xff;
> + /* 8bit read works with and without FIFO */
> + *dev->buf = readb_relaxed(dev->base + AT91_TWI_RHR);
> --dev->buf_len;
>
> /* return if aborting, we only needed to read RHR to clear RXRDY*/
> @@ -332,7 +390,7 @@ static void at91_twi_read_data_dma_callback(void *data)
> struct at91_twi_dev *dev = (struct at91_twi_dev *)data;
> unsigned ier = AT91_TWI_TXCOMP;
>
> - dma_unmap_single(dev->dev, sg_dma_address(&dev->dma.sg),
> + dma_unmap_single(dev->dev, sg_dma_address(&dev->dma.sg[0]),
> dev->buf_len, DMA_FROM_DEVICE);
>
> if (!dev->pdata->has_alt_cmd) {
> @@ -364,10 +422,24 @@ static void at91_twi_read_data_dma(struct at91_twi_dev *dev)
> }
> dma->buf_mapped = true;
> at91_twi_irq_restore(dev);
> - dma->sg.dma_address = dma_addr;
> - sg_dma_len(&dma->sg) = buf_len;
>
> - rxdesc = dmaengine_prep_slave_sg(chan_rx, &dma->sg, 1, DMA_DEV_TO_MEM,
> + if (dev->fifo_size && IS_ALIGNED(buf_len, 4)) {
> + unsigned fifo_mr;
> +
> + /*
> + * DMA controller is triggered when at least 4 data can be
> + * read from the RX FIFO
> + */
> + fifo_mr = at91_twi_read(dev, AT91_TWI_FMR);
> + fifo_mr &= ~AT91_TWI_FMR_RXRDYM_MASK;
> + fifo_mr |= AT91_TWI_FMR_RXRDYM(AT91_TWI_FOUR_DATA);
> + at91_twi_write(dev, AT91_TWI_FMR, fifo_mr);
> + }
> +
> + sg_dma_len(&dma->sg[0]) = buf_len;
> + sg_dma_address(&dma->sg[0]) = dma_addr;
> +
> + rxdesc = dmaengine_prep_slave_sg(chan_rx, dma->sg, 1, DMA_DEV_TO_MEM,
> DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
> if (!rxdesc) {
> dev_err(dev->dev, "dma prep slave sg failed\n");
> @@ -468,6 +540,21 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> reinit_completion(&dev->cmd_complete);
> dev->transfer_status = 0;
>
> + if (dev->fifo_size) {
> + unsigned fifo_mr = at91_twi_read(dev, AT91_TWI_FMR);
> +
> + /* Reset FIFO mode register */
> + fifo_mr &= ~(AT91_TWI_FMR_TXRDYM_MASK |
> + AT91_TWI_FMR_RXRDYM_MASK);
> + fifo_mr |= AT91_TWI_FMR_TXRDYM(AT91_TWI_ONE_DATA);
> + fifo_mr |= AT91_TWI_FMR_RXRDYM(AT91_TWI_ONE_DATA);
> + at91_twi_write(dev, AT91_TWI_FMR, fifo_mr);
> +
> + /* Flush FIFOs */
> + at91_twi_write(dev, AT91_TWI_CR,
> + AT91_TWI_THRCLR | AT91_TWI_RHRCLR);
> + }
> +
> if (!dev->buf_len) {
> at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_QUICK);
> at91_twi_write(dev, AT91_TWI_IER, AT91_TWI_TXCOMP);
> @@ -538,7 +625,8 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
> ret = -EIO;
> goto error;
> }
> - if (has_alt_cmd && (dev->transfer_status & AT91_TWI_LOCK)) {
> + if ((has_alt_cmd || dev->fifo_size) &&
> + (dev->transfer_status & AT91_TWI_LOCK)) {
> dev_err(dev->dev, "tx locked\n");
> ret = -EIO;
> goto error;
> @@ -557,7 +645,8 @@ error:
> /* first stop DMA transfer if still in progress */
> at91_twi_dma_cleanup(dev);
> /* then flush THR/FIFO and unlock TX if locked */
> - if (has_alt_cmd && (dev->transfer_status & AT91_TWI_LOCK)) {
> + if ((has_alt_cmd || dev->fifo_size) &&
> + (dev->transfer_status & AT91_TWI_LOCK)) {
> dev_dbg(dev->dev, "unlock tx\n");
> at91_twi_write(dev, AT91_TWI_CR,
> AT91_TWI_THRCLR | AT91_TWI_LOCKCLR);
> @@ -745,13 +834,32 @@ static int at91_twi_configure_dma(struct at91_twi_dev *dev, u32 phy_addr)
> int ret = 0;
> struct dma_slave_config slave_config;
> struct at91_twi_dma *dma = &dev->dma;
> + enum dma_slave_buswidth addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> +
> + /*
> + * The actual width of the access will be chosen in
> + * dmaengine_prep_slave_sg():
> + * for each buffer in the scatter-gather list, if its size is aligned
> + * to addr_width then addr_width accesses will be performed to transfer
> + * the buffer. On the other hand, if the buffer size is not aligned to
> + * addr_width then the buffer is transferred using single byte accesses.
> + * Please refer to the Atmel eXtended DMA controller driver.
> + * When FIFOs are used, the TXRDYM threshold can always be set to
> + * trigger the XDMAC when at least 4 data can be written into the TX
> + * FIFO, even if single byte accesses are performed.
> + * However the RXRDYM threshold must be set to fit the access width,
> + * deduced from buffer length, so the XDMAC is triggered properly to
> + * read data from the RX FIFO.
> + */
> + if (dev->fifo_size)
> + addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
>
> memset(&slave_config, 0, sizeof(slave_config));
> slave_config.src_addr = (dma_addr_t)phy_addr + AT91_TWI_RHR;
> - slave_config.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> + slave_config.src_addr_width = addr_width;
> slave_config.src_maxburst = 1;
> slave_config.dst_addr = (dma_addr_t)phy_addr + AT91_TWI_THR;
> - slave_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> + slave_config.dst_addr_width = addr_width;
> slave_config.dst_maxburst = 1;
> slave_config.device_fc = false;
>
> @@ -783,7 +891,7 @@ static int at91_twi_configure_dma(struct at91_twi_dev *dev, u32 phy_addr)
> goto error;
> }
>
> - sg_init_table(&dma->sg, 1);
> + sg_init_table(dma->sg, 2);
> dma->buf_mapped = false;
> dma->xfer_in_progress = false;
> dev->use_dma = true;
> @@ -870,6 +978,10 @@ static int at91_twi_probe(struct platform_device *pdev)
> }
>
> dev_info(dev->dev, "version: 0x%x\n", at91_twi_read(dev, AT91_TWI_VER));
> + if (!of_property_read_u32(pdev->dev.of_node, "atmel,fifo-size",
> + &dev->fifo_size)) {
> + dev_info(dev->dev, "Using FIFO (%u data)\n", dev->fifo_size);
> + }
>
> rc = of_property_read_u32(dev->dev->of_node, "clock-frequency",
> &bus_clk_rate);
> --
> 1.8.2.2
>

Ludovic
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Next message: David Jander: "[PATCH] mmc: core: Fix off-by-one error in mmc_do_calc_max_discard()"
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