linux-kernel - Re: [PATCH] spi: imx: keep dma request disabled before dma transfer setup

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Message-ID: <aPuKKrb56CLLeYTb@lizhi-Precision-Tower-5810>
Date: Fri, 24 Oct 2025 10:16:10 -0400
From: Frank Li <Frank.li@....com>
To: carlos.song@....com
Cc: broonie@...nel.org, shawnguo@...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] spi: imx: keep dma request disabled before dma transfer
 setup

On Fri, Oct 24, 2025 at 01:53:20PM +0800, carlos.song@....com wrote:
> From: Robin Gong <yibin.gong@....com>
>
> Since sdma hardware configure postpone to transfer phase, have to disable
> dma request before dma transfer setup because there is a hardware
> limitation on sdma event enable(ENBLn) as below:

Due to a hardware limitation on SDMA event enable (ENBLn), the DMA request
must remain disabled until the DMA transfer setup is complete.

Ref spec section [...]
>
> "It is thus essential for the Arm platform to program them before any DMA
>  request is triggered to the SDMA, otherwise an unpredictable combination
>  of channels may be started."

SDMA hardware configuration is postponed to the transfer phase, so enabling
the DMA request too early may cause unpredictable channel activation. Then
keep dma request disabled before dma transfer setup.

Frank
>
> Signed-off-by: Carlos Song <carlos.song@....com>
> Signed-off-by: Robin Gong <yibin.gong@....com>
> ---
>  drivers/spi/spi-imx.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
> index cd40db61d8d1..765ea507dd8d 100644
> --- a/drivers/spi/spi-imx.c
> +++ b/drivers/spi/spi-imx.c
> @@ -529,9 +529,15 @@ static void mx51_ecspi_trigger(struct spi_imx_data *spi_imx)
>  {
>  	u32 reg;
>
> -	reg = readl(spi_imx->base + MX51_ECSPI_CTRL);
> -	reg |= MX51_ECSPI_CTRL_XCH;
> -	writel(reg, spi_imx->base + MX51_ECSPI_CTRL);
> +	if (spi_imx->usedma) {
> +		reg = readl(spi_imx->base + MX51_ECSPI_DMA);
> +		reg |= MX51_ECSPI_DMA_TEDEN | MX51_ECSPI_DMA_RXDEN;
> +		writel(reg, spi_imx->base + MX51_ECSPI_DMA);
> +	} else {
> +		reg = readl(spi_imx->base + MX51_ECSPI_CTRL);
> +		reg |= MX51_ECSPI_CTRL_XCH;
> +		writel(reg, spi_imx->base + MX51_ECSPI_CTRL);
> +	}
>  }
>
>  static void mx51_ecspi_disable(struct spi_imx_data *spi_imx)
> @@ -772,7 +778,6 @@ static void mx51_setup_wml(struct spi_imx_data *spi_imx)
>  	writel(MX51_ECSPI_DMA_RX_WML(spi_imx->wml - 1) |
>  		MX51_ECSPI_DMA_TX_WML(tx_wml) |
>  		MX51_ECSPI_DMA_RXT_WML(spi_imx->wml) |
> -		MX51_ECSPI_DMA_TEDEN | MX51_ECSPI_DMA_RXDEN |
>  		MX51_ECSPI_DMA_RXTDEN, spi_imx->base + MX51_ECSPI_DMA);
>  }
>
> @@ -1539,6 +1544,8 @@ static int spi_imx_dma_transfer(struct spi_imx_data *spi_imx,
>  	reinit_completion(&spi_imx->dma_tx_completion);
>  	dma_async_issue_pending(controller->dma_tx);
>
> +	spi_imx->devtype_data->trigger(spi_imx);
> +
>  	transfer_timeout = spi_imx_calculate_timeout(spi_imx, transfer->len);
>
>  	/* Wait SDMA to finish the data transfer.*/
> --
> 2.34.1
>