staging: mt7621-mmc: Check for nonzero number of scatterlist entries

[ Upstream commit d4223e06 ]

The buffer descriptor setup loop is correct only if it is setting up at
least one bd struct.  Besides, there is an error if dma_map_sg() returns
0, which is possible and must be handled.

Additionally, remove the BUG_ON() checking sglen, which is unnecessary
because we configure DMA with that constraint during init.
Signed-off-by: George Hilliard <thirtythreeforty@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/staging/mt7621-mmc/sd.c

@@ -596,8 +596,6 @@ static void msdc_dma_setup(struct msdc_host *host, struct msdc_dma *dma,
 	struct bd *bd;
 	u32 j;
 
-	BUG_ON(sglen > MAX_BD_NUM); /* not support currently */
-
 	gpd = dma->gpd;
 	bd  = dma->bd;
 
@@ -692,6 +690,13 @@ static int msdc_do_request(struct mmc_host *mmc, struct mmc_request *mrq)
 		data->sg_count = dma_map_sg(mmc_dev(mmc), data->sg,
 					    data->sg_len,
 					    mmc_get_dma_dir(data));
+
+		if (data->sg_count == 0) {
+			dev_err(mmc_dev(host->mmc), "failed to map DMA for transfer\n");
+			data->error = -ENOMEM;
+			goto done;
+		}
+
 		msdc_dma_setup(host, &host->dma, data->sg,
 			       data->sg_count);