linux-kernel - Re: [PATCH 5/6] spi: imx: support dynamic burst length for ECSPI DMA mode

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Message-ID: <20251126-mahogany-skunk-of-drama-db31a4-mkl@pengutronix.de>
Date: Wed, 26 Nov 2025 09:27:57 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Carlos Song <carlos.song@....com>
Cc: broonie@...nel.org, frank.li@....com, hawnguo@...nel.org, 
	s.hauer@...gutronix.de, kernel@...gutronix.de, festevam@...il.com, 
	linux-spi@...r.kernel.org, imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] spi: imx: support dynamic burst length for ECSPI DMA
 mode

On 25.11.2025 18:06:17, Carlos Song wrote:
> +static int spi_imx_dma_data_prepare(struct spi_imx_data *spi_imx,
> +				    struct spi_transfer *transfer,
> +				    bool word_delay)
> +{
> +	u32 pre_bl, tail_bl;
> +	u32 ctrl;
> +	int ret;
> +
> +	/*
> +	 * ECSPI supports a maximum burst of 512 bytes. When xfer->len exceeds 512
> +	 * and is not a multiple of 512, a tail transfer is required. In this case,
> +	 * an extra DMA request is issued for the remaining data.
> +	 */
> +	ctrl = readl(spi_imx->base + MX51_ECSPI_CTRL);
> +	if (word_delay) {
> +		/*
> +		 * When SPI IMX need to support word delay, according to "Sample Period Control
> +		 * Register" shows, The Sample Period Control Register (ECSPI_PERIODREG)
> +		 * provides software a way to insert delays (wait states) between consecutive
> +		 * SPI transfers. As a result, ECSPI can only transfer one word per frame, and
> +		 * the delay occurs between frames.
> +		 */
> +		spi_imx->dma_package_num = 1;
> +		pre_bl = spi_imx->bits_per_word - 1;
> +	} else if (transfer->len <= MX51_ECSPI_CTRL_MAX_BURST) {
> +		spi_imx->dma_package_num = 1;
> +		pre_bl = transfer->len * BITS_PER_BYTE - 1;
> +	} else if (!(transfer->len % MX51_ECSPI_CTRL_MAX_BURST)) {
> +		spi_imx->dma_package_num = 1;
> +		pre_bl = MX51_ECSPI_CTRL_MAX_BURST * BITS_PER_BYTE - 1;
> +	} else {
> +		spi_imx->dma_package_num = 2;
> +		pre_bl = MX51_ECSPI_CTRL_MAX_BURST * BITS_PER_BYTE - 1;
> +		tail_bl = (transfer->len % MX51_ECSPI_CTRL_MAX_BURST) * BITS_PER_BYTE - 1;
> +	}
> +
> +	spi_imx->dma_data = kmalloc_array(spi_imx->dma_package_num,
> +					  sizeof(struct dma_data_package),
> +					  GFP_KERNEL | __GFP_ZERO);
> +	if (!spi_imx->dma_data) {
> +		dev_err(spi_imx->dev, "Failed to allocate DMA package buffer!\n");
> +		return -ENOMEM;
> +	}
> +
> +	if (spi_imx->dma_package_num == 1) {
> +		ctrl &= ~MX51_ECSPI_CTRL_BL_MASK;
> +		ctrl |= pre_bl << MX51_ECSPI_CTRL_BL_OFFSET;
> +		spi_imx->dma_data[0].cmd_word = ctrl;
> +		spi_imx->dma_data[0].data_len = transfer->len;
> +		ret = spi_imx_dma_tx_data_handle(spi_imx, &spi_imx->dma_data[0], transfer->tx_buf,
> +						 word_delay);
> +		if (ret) {
> +			kfree(spi_imx->dma_data);
> +			return ret;
> +		}
> +	} else {
> +		ctrl &= ~MX51_ECSPI_CTRL_BL_MASK;
> +		ctrl |= pre_bl << MX51_ECSPI_CTRL_BL_OFFSET;
> +		spi_imx->dma_data[0].cmd_word = ctrl;
> +		spi_imx->dma_data[0].data_len = DIV_ROUND_DOWN_ULL(transfer->len,
> +								   MX51_ECSPI_CTRL_MAX_BURST)
> +								   * MX51_ECSPI_CTRL_MAX_BURST;

What mathematical operation do you want to do? Why do you use a 64 bit
div? What about round_down()?

> +		ret = spi_imx_dma_tx_data_handle(spi_imx, &spi_imx->dma_data[0], transfer->tx_buf,
> +						 false);
> +		if (ret) {
> +			kfree(spi_imx->dma_data);
> +			return ret;
> +		}
> +
> +		ctrl &= ~MX51_ECSPI_CTRL_BL_MASK;
> +		ctrl |= tail_bl << MX51_ECSPI_CTRL_BL_OFFSET;
> +		spi_imx->dma_data[1].cmd_word = ctrl;
> +		spi_imx->dma_data[1].data_len = transfer->len % MX51_ECSPI_CTRL_MAX_BURST;
> +		ret = spi_imx_dma_tx_data_handle(spi_imx, &spi_imx->dma_data[1],
> +						 transfer->tx_buf + spi_imx->dma_data[0].data_len,
> +						 false);
> +		if (ret) {
> +			kfree(spi_imx->dma_data[0].dma_tx_buf);
> +			kfree(spi_imx->dma_data[0].dma_rx_buf);
> +			kfree(spi_imx->dma_data);
> +		}
> +	}
> +
> +	return 0;
> +}

regards,
Marc

--
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
Vertretung Nürnberg              | Phone: +49-5121-206917-129 |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-9   |

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