spi: dw: Add support for the Canaan K210 SoC SPI

The Canaan Kendryte K210 RISC-V SoC includes a DW apb_ssi v4 controller
which is documented to have a 32 words deep TX and RX FIFO. The FIFO
length detection in spi_hw_init() correctly detects this value.
However, when the controller RX FIFO is filled up to 32 entries
(RXFLR = 32), an RX FIFO overrun error occurs. This likely due to a
hardware bug which can be avoided by force setting the fifo_len field of
struct dw_spi to 31.

Define the dw_spi_canaan_k210_init() function to force set fifo_len to
31 when the device node compatible string is "canaan,k210-spi".

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Acked-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/20201206011817.11700-4-damien.lemoal@wdc.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-dw-mmio.c

@@ -222,6 +222,21 @@ static int dw_spi_keembay_init(struct platform_device *pdev,
 	return 0;
 }
 
+static int dw_spi_canaan_k210_init(struct platform_device *pdev,
+				   struct dw_spi_mmio *dwsmmio)
+{
+	/*
+	 * The Canaan Kendryte K210 SoC DW apb_ssi v4 spi controller is
+	 * documented to have a 32 word deep TX and RX FIFO, which
+	 * spi_hw_init() detects. However, when the RX FIFO is filled up to
+	 * 32 entries (RXFLR = 32), an RX FIFO overrun error occurs. Avoid this
+	 * problem by force setting fifo_len to 31.
+	 */
+	dwsmmio->dws.fifo_len = 31;
+
+	return 0;
+}
+
 static int dw_spi_mmio_probe(struct platform_device *pdev)
 {
 	int (*init_func)(struct platform_device *pdev,
@@ -335,6 +350,7 @@ static const struct of_device_id dw_spi_mmio_of_match[] = {
 	{ .compatible = "snps,dwc-ssi-1.01a", .data = dw_spi_dwc_ssi_init},
 	{ .compatible = "intel,keembay-ssi", .data = dw_spi_keembay_init},
 	{ .compatible = "microchip,sparx5-spi", dw_spi_mscc_sparx5_init},
+	{ .compatible = "canaan,k210-spi", dw_spi_canaan_k210_init},
 	{ /* end of table */}
 };
 MODULE_DEVICE_TABLE(of, dw_spi_mmio_of_match);