On Fri, May 15, 2020 at 01:47:49PM +0300, Serge Semin wrote:
> Each channel of DMA controller may have a limited length of burst
> transaction (number of IO operations performed at ones in a single
> DMA client request). This parameter can be used to setup the most
> optimal DMA Tx/Rx data level values. In order to avoid the Tx buffer
> overrun we can set the DMA Tx level to be of FIFO depth minus the
> maximum burst transactions length. To prevent the Rx buffer underflow
> the DMA Rx level should be set to the maximum burst transactions length.
> This commit setups the DMA channels and the DW SPI DMA Tx/Rx levels
> in accordance with these rules.
It's good one, but see my comments.
I think this patch should go before previous one.
(and without changes regarding FIFO length)
> +static void mid_spi_maxburst_init(struct dw_spi *dws)
> +{
> + struct dma_slave_caps caps;
> + u32 max_burst, def_burst;
> + int ret;
> +
> + def_burst = dws->fifo_len / 2;
> +
> + ret = dma_get_slave_caps(dws->rxchan, &caps);
> + if (!ret && caps.max_burst)
> + max_burst = caps.max_burst;
> + else
> + max_burst = RX_BURST_LEVEL;
> +
> + dws->rxburst = (def_burst > max_burst) ? max_burst : def_burst;
min() ?
> +
> + ret = dma_get_slave_caps(dws->txchan, &caps);
> + if (!ret && caps.max_burst)
> + max_burst = caps.max_burst;
> + else
> + max_burst = TX_BURST_LEVEL;
> +
> + dws->txburst = (def_burst > max_burst) ? max_burst : def_burst;
Ditto.
> +}
> +
> static int mid_spi_dma_init_mfld(struct device *dev, struct dw_spi *dws)
> {
> struct dw_dma_slave slave = {0};
> @@ -67,6 +92,8 @@ static int mid_spi_dma_init_mfld(struct device *dev, struct dw_spi *dws)
> dws->master->dma_rx = dws->rxchan;
> dws->master->dma_tx = dws->txchan;
>
> + mid_spi_maxburst_init(dws);
> +
> return 0;
>
> free_rxchan:
> @@ -92,6 +119,8 @@ static int mid_spi_dma_init_generic(struct device *dev, struct dw_spi *dws)
> dws->master->dma_rx = dws->rxchan;
> dws->master->dma_tx = dws->txchan;
>
> + mid_spi_maxburst_init(dws);
> +
> return 0;
> }
>
> @@ -195,7 +224,7 @@ static struct dma_async_tx_descriptor *dw_spi_dma_prepare_tx(struct dw_spi *dws,
> memset(&txconf, 0, sizeof(txconf));
> txconf.direction = DMA_MEM_TO_DEV;
> txconf.dst_addr = dws->dma_addr;
> - txconf.dst_maxburst = TX_BURST_LEVEL;
> + txconf.dst_maxburst = dws->txburst;
> txconf.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
> txconf.dst_addr_width = convert_dma_width(dws->n_bytes);
> txconf.device_fc = false;
> @@ -268,7 +297,7 @@ static struct dma_async_tx_descriptor *dw_spi_dma_prepare_rx(struct dw_spi *dws,
> memset(&rxconf, 0, sizeof(rxconf));
> rxconf.direction = DMA_DEV_TO_MEM;
> rxconf.src_addr = dws->dma_addr;
> - rxconf.src_maxburst = RX_BURST_LEVEL;
> + rxconf.src_maxburst = dws->rxburst;
> rxconf.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
> rxconf.src_addr_width = convert_dma_width(dws->n_bytes);
> rxconf.device_fc = false;
> @@ -293,8 +322,8 @@ static int mid_spi_dma_setup(struct dw_spi *dws, struct spi_transfer *xfer)
> {
> u16 imr = 0, dma_ctrl = 0;
>
> - dw_writel(dws, DW_SPI_DMARDLR, RX_BURST_LEVEL - 1);
> - dw_writel(dws, DW_SPI_DMATDLR, dws->fifo_len - TX_BURST_LEVEL);
> + dw_writel(dws, DW_SPI_DMARDLR, dws->rxburst - 1);
> + dw_writel(dws, DW_SPI_DMATDLR, dws->fifo_len - dws->txburst);
>
> if (xfer->tx_buf) {
> dma_ctrl |= SPI_DMA_TDMAE;
...
> /* DMA info */
> struct dma_chan *txchan;
> + u32 txburst;
> struct dma_chan *rxchan;
> + u32 rxburst;
Leave u32 together, it may be optimal on 64-bit architectures where ABIs require padding.
--
With Best Regards,
Andy Shevchenko
