It was <2020-08-19 śro 14:48>, when Krzysztof Kozlowski wrote:

On Wed, Aug 19, 2020 at 02:32:06PM +0200, Łukasz Stelmach wrote:

quoted

Signed-off-by: Łukasz Stelmach <l.stelmach@samsung.com>
---
 drivers/spi/spi-s3c64xx.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

Oh, come on, stop fixing the same local issue without fixing bigger
picture... or at least documenting why bigger picture does not have to be
fixed and simple 'return' is enough.

That's the third, same fix for the same problem.

https://lore.kernel.org/lkml/20190314064202.14864-1-kjlu@umn.edu/ (local)
https://lore.kernel.org/lkml/20170207204520.h2eo3yn5kge56lk7@kozik-lap/ (local)

No wonder. There is a possible NULL dereference below. Now at least we
know something about conditions that led to this.

Should I drop the entire patch, or just the dmaengine_prep_slave_sg() part?

quoted

diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
index 505789f91fdf..27d77600a820 100644
--- a/drivers/spi/spi-s3c64xx.c
+++ b/drivers/spi/spi-s3c64xx.c

@@ -273,6 +273,7 @@ static void prepare_dma(struct s3c64xx_spi_dma_data *dma,
 	struct s3c64xx_spi_driver_data *sdd;
 	struct dma_slave_config config;
 	struct dma_async_tx_descriptor *desc;
+	int ret;
 
 	memset(&config, 0, sizeof(config));
 

@@ -296,11 +297,22 @@ static void prepare_dma(struct s3c64xx_spi_dma_data *dma,
 
 	desc = dmaengine_prep_slave_sg(dma->ch, sgt->sgl, sgt->nents,
 				       dma->direction, DMA_PREP_INTERRUPT);
+	if (!desc) {
+		dev_err(&sdd->pdev->dev, "unable to prepare %s scatterlist",
+			dma->direction == DMA_DEV_TO_MEM ? "rx" : "tx");
+		return;
+	}
 
 	desc->callback = s3c64xx_spi_dmacb;
 	desc->callback_param = dma;
 
 	dma->cookie = dmaengine_submit(desc);
+	ret = dma_submit_error(dma->cookie);
+	if (ret) {
+		dev_err(&sdd->pdev->dev, "dmaengine_submit() failed %d", ret);
+		return;
+	}
+
 	dma_async_issue_pending(dma->ch);
 }
 

-- 
2.26.2

-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics