spi: spi-omap2-mcspi: Handle DMA size restriction on AM65x

On AM654, McSPI can only support 4K - 1 bytes per transfer when DMA is
enabled. Therefore populate master->max_transfer_size callback to
inform client drivers of this restriction when DMA channels are
available.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200204124816.16735-2-vigneshr@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-omap2-mcspi.c

@@ -130,6 +130,7 @@ struct omap2_mcspi {
 	int			fifo_depth;
 	bool			slave_aborted;
 	unsigned int		pin_dir:1;
+	size_t			max_xfer_len;
 };
 
 struct omap2_mcspi_cs {
@@ -1305,6 +1306,18 @@ static bool omap2_mcspi_can_dma(struct spi_master *master,
 	return (xfer->len >= DMA_MIN_BYTES);
 }
 
+static size_t omap2_mcspi_max_xfer_size(struct spi_device *spi)
+{
+	struct omap2_mcspi *mcspi = spi_master_get_devdata(spi->master);
+	struct omap2_mcspi_dma *mcspi_dma =
+		&mcspi->dma_channels[spi->chip_select];
+
+	if (mcspi->max_xfer_len && mcspi_dma->dma_rx)
+		return mcspi->max_xfer_len;
+
+	return SIZE_MAX;
+}
+
 static int omap2_mcspi_controller_setup(struct omap2_mcspi *mcspi)
 {
 	struct spi_master	*master = mcspi->master;
@@ -1373,6 +1386,11 @@ static struct omap2_mcspi_platform_config omap4_pdata = {
 	.regs_offset = OMAP4_MCSPI_REG_OFFSET,
 };
 
+static struct omap2_mcspi_platform_config am654_pdata = {
+	.regs_offset = OMAP4_MCSPI_REG_OFFSET,
+	.max_xfer_len = SZ_4K - 1,
+};
+
 static const struct of_device_id omap_mcspi_of_match[] = {
 	{
 		.compatible = "ti,omap2-mcspi",
@@ -1382,6 +1400,10 @@ static const struct of_device_id omap_mcspi_of_match[] = {
 		.compatible = "ti,omap4-mcspi",
 		.data = &omap4_pdata,
 	},
+	{
+		.compatible = "ti,am654-mcspi",
+		.data = &am654_pdata,
+	},
 	{ },
 };
 MODULE_DEVICE_TABLE(of, omap_mcspi_of_match);
@@ -1439,6 +1461,10 @@ static int omap2_mcspi_probe(struct platform_device *pdev)
 		mcspi->pin_dir = pdata->pin_dir;
 	}
 	regs_offset = pdata->regs_offset;
+	if (pdata->max_xfer_len) {
+		mcspi->max_xfer_len = pdata->max_xfer_len;
+		master->max_transfer_size = omap2_mcspi_max_xfer_size;
+	}
 
 	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	mcspi->base = devm_ioremap_resource(&pdev->dev, r);

include/linux/platform_data/spi-omap2-mcspi.h

@@ -11,6 +11,7 @@ struct omap2_mcspi_platform_config {
 	unsigned short	num_cs;
 	unsigned int regs_offset;
 	unsigned int pin_dir:1;
+	size_t max_xfer_len;
 };
 
 struct omap2_mcspi_device_config {