i2c: imx: support DMA defer probing

JIRA: https://issues.redhat.com/browse/RHEL-116101

commit d9a13c0
Author: Carlos Song <carlos.song@nxp.com>
Date:   Thu Dec 26 14:25:21 2024 +0800

    i2c: imx: support DMA defer probing

    Return -EPROBE_DEFER when dma_request_slave_channel() because DMA driver
    have not ready yet.

    Move i2c_imx_dma_request() before registering I2C adapter to avoid
    infinite loop of .probe() calls to the same driver, see "e8c220fac415
    Revert "i2c: imx: improve the error handling in i2c_imx_dma_request()""
    and "Documentation/driver-api/driver-model/driver.rst".

    Use CPU mode to avoid stuck registering i2c adapter when DMA resources
    are unavailable.

    Signed-off-by: Carlos Song <carlos.song@nxp.com>
    Signed-off-by: Clark Wang <xiaoning.wang@nxp.com>
    Acked-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
    Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
    Link: https://lore.kernel.org/r/20241226062521.1004809-1-carlos.song@nxp.com
    Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

Signed-off-by: Jared Kangas <jkangas@redhat.com>

Author: rh-jkangas

drivers/i2c/busses/i2c-imx.c

@@ -397,17 +397,16 @@ static void i2c_imx_reset_regs(struct imx_i2c_struct *i2c_imx)
 }
 
 /* Functions for DMA support */
-static void i2c_imx_dma_request(struct imx_i2c_struct *i2c_imx,
-						dma_addr_t phy_addr)
+static int i2c_imx_dma_request(struct imx_i2c_struct *i2c_imx, dma_addr_t phy_addr)
 {
 	struct imx_i2c_dma *dma;
 	struct dma_slave_config dma_sconfig;
-	struct device *dev = &i2c_imx->adapter.dev;
+	struct device *dev = i2c_imx->adapter.dev.parent;
 	int ret;
 
 	dma = devm_kzalloc(dev, sizeof(*dma), GFP_KERNEL);
 	if (!dma)
-		return;
+		return -ENOMEM;
 
 	dma->chan_tx = dma_request_chan(dev, "tx");
 	if (IS_ERR(dma->chan_tx)) {
@@ -452,14 +451,16 @@ static void i2c_imx_dma_request(struct imx_i2c_struct *i2c_imx,
 	dev_info(dev, "using %s (tx) and %s (rx) for DMA transfers\n",
 		dma_chan_name(dma->chan_tx), dma_chan_name(dma->chan_rx));
 
-	return;
+	return 0;
 
 fail_rx:
 	dma_release_channel(dma->chan_rx);
 fail_tx:
 	dma_release_channel(dma->chan_tx);
 fail_al:
 	devm_kfree(dev, dma);
+
+	return ret;
 }
 
 static void i2c_imx_dma_callback(void *arg)
@@ -1802,6 +1803,22 @@ static int i2c_imx_probe(struct platform_device *pdev)
 	if (ret == -EPROBE_DEFER)
 		goto clk_notifier_unregister;
 
+	/*
+	 * DMA mode should be optional for I2C, when encountering DMA errors,
+	 * no need to exit I2C probe. Only print warning to show DMA error and
+	 * use PIO mode directly to ensure I2C bus available as much as possible.
+	 */
+	ret = i2c_imx_dma_request(i2c_imx, phy_addr);
+	if (ret) {
+		if (ret == -EPROBE_DEFER)
+			goto clk_notifier_unregister;
+		else if (ret == -ENODEV)
+			dev_dbg(&pdev->dev, "Only use PIO mode\n");
+		else
+			dev_warn(&pdev->dev, "Failed to setup DMA (%pe), only use PIO mode\n",
+				 ERR_PTR(ret));
+	}
+
 	/* Add I2C adapter */
 	ret = i2c_add_numbered_adapter(&i2c_imx->adapter);
 	if (ret < 0)
@@ -1816,9 +1833,6 @@ static int i2c_imx_probe(struct platform_device *pdev)
 		i2c_imx->adapter.name);
 	dev_info(&i2c_imx->adapter.dev, "IMX I2C adapter registered\n");
 
-	/* Init DMA config if supported */
-	i2c_imx_dma_request(i2c_imx, phy_addr);
-
 	return 0;   /* Return OK */
 
 clk_notifier_unregister: