spi: s3c64xx: Fix large transfers with DMA

The COUNT_VALUE in the PACKET_CNT register is 16-bit so the maximum
value is 65535.  Asking the driver to transfer a larger size currently
leads to the DMA transfer timing out.  Implement ->max_transfer_size()
and have the core split the transfer as needed.

Fixes: 230d42d422e7 ("spi: Add s3c64xx SPI Controller driver")
Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Link: https://lore.kernel.org/r/20220927112117.77599-5-vincent.whitchurch@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
index 651c35d..71d324e 100644 (file)
--- a/drivers/spi/spi-s3c64xx.c
+++ b/drivers/spi/spi-s3c64xx.c
@@ -84,6 +84,7 @@
 #define S3C64XX_SPI_ST_TX_FIFORDY              (1<<0)
 
 #define S3C64XX_SPI_PACKET_CNT_EN              (1<<16)
+#define S3C64XX_SPI_PACKET_CNT_MASK            GENMASK(15, 0)
 
 #define S3C64XX_SPI_PND_TX_UNDERRUN_CLR                (1<<4)
 #define S3C64XX_SPI_PND_TX_OVERRUN_CLR         (1<<3)
@@ -711,6 +712,13 @@ static int s3c64xx_spi_prepare_message(struct spi_master *master,
        return 0;
 }
 
+static size_t s3c64xx_spi_max_transfer_size(struct spi_device *spi)
+{
+       struct spi_controller *ctlr = spi->controller;
+
+       return ctlr->can_dma ? S3C64XX_SPI_PACKET_CNT_MASK : SIZE_MAX;
+}
+
 static int s3c64xx_spi_transfer_one(struct spi_master *master,
                                    struct spi_device *spi,
                                    struct spi_transfer *xfer)
@@ -1152,6 +1160,7 @@ static int s3c64xx_spi_probe(struct platform_device *pdev)
        master->unprepare_transfer_hardware = s3c64xx_spi_unprepare_transfer;
        master->prepare_message = s3c64xx_spi_prepare_message;
        master->transfer_one = s3c64xx_spi_transfer_one;
+       master->max_transfer_size = s3c64xx_spi_max_transfer_size;
        master->num_chipselect = sci->num_cs;
        master->use_gpio_descriptors = true;
        master->dma_alignment = 8;