media: atmel: atmel-isc: limit incoming pixels per frame

This will limit the incoming pixels per frame from the sensor.
Currently, the ISC will stop sampling the frame only when the vsync/hsync
are detected.
If we misconfigure the resolution in the sensor w.r.t. resolution in the ISC,
the buffer used for DMA in the ISC will be smaller than the number of pixels
that the ISC DMA engine will copy.
In this case it happens that the DMA will overwrite parts of the memory which
should not be written, leading to memory corruption.
To avoid this situation, use the PFE CFG1 and PFE CFG2 registers, which crop
the incoming frame to the resolution that we configure.
This way the DMA engine will never write more data than we expect it to.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/platform/atmel/atmel-isc-regs.h

@@ -37,6 +37,25 @@
 #define ISC_PFG_CFG0_BPS_TWELVE (0x0 << 28)
 #define ISC_PFE_CFG0_BPS_MASK   GENMASK(30, 28)
 
+#define ISC_PFE_CFG0_COLEN	BIT(12)
+#define ISC_PFE_CFG0_ROWEN	BIT(13)
+
+/* ISC Parallel Front End Configuration 1 Register */
+#define ISC_PFE_CFG1    0x00000010
+
+#define ISC_PFE_CFG1_COLMIN(v)		((v))
+#define ISC_PFE_CFG1_COLMIN_MASK	GENMASK(15, 0)
+#define ISC_PFE_CFG1_COLMAX(v)		((v) << 16)
+#define ISC_PFE_CFG1_COLMAX_MASK	GENMASK(31, 16)
+
+/* ISC Parallel Front End Configuration 2 Register */
+#define ISC_PFE_CFG2    0x00000014
+
+#define ISC_PFE_CFG2_ROWMIN(v)		((v))
+#define ISC_PFE_CFG2_ROWMIN_MASK	GENMASK(15, 0)
+#define ISC_PFE_CFG2_ROWMAX(v)		((v) << 16)
+#define ISC_PFE_CFG2_ROWMAX_MASK	GENMASK(31, 16)
+
 /* ISC Clock Enable Register */
 #define ISC_CLKEN               0x00000018
 

drivers/media/platform/atmel/atmel-isc.c

@@ -721,6 +721,40 @@ static void isc_start_dma(struct isc_device *isc)
 	u32 sizeimage = isc->fmt.fmt.pix.sizeimage;
 	u32 dctrl_dview;
 	dma_addr_t addr0;
+	u32 h, w;
+
+	h = isc->fmt.fmt.pix.height;
+	w = isc->fmt.fmt.pix.width;
+
+	/*
+	 * In case the sensor is not RAW, it will output a pixel (12-16 bits)
+	 * with two samples on the ISC Data bus (which is 8-12)
+	 * ISC will count each sample, so, we need to multiply these values
+	 * by two, to get the real number of samples for the required pixels.
+	 */
+	if (!ISC_IS_FORMAT_RAW(isc->config.sd_format->mbus_code)) {
+		h <<= 1;
+		w <<= 1;
+	}
+
+	/*
+	 * We limit the column/row count that the ISC will output according
+	 * to the configured resolution that we want.
+	 * This will avoid the situation where the sensor is misconfigured,
+	 * sending more data, and the ISC will just take it and DMA to memory,
+	 * causing corruption.
+	 */
+	regmap_write(regmap, ISC_PFE_CFG1,
+		     (ISC_PFE_CFG1_COLMIN(0) & ISC_PFE_CFG1_COLMIN_MASK) |
+		     (ISC_PFE_CFG1_COLMAX(w - 1) & ISC_PFE_CFG1_COLMAX_MASK));
+
+	regmap_write(regmap, ISC_PFE_CFG2,
+		     (ISC_PFE_CFG2_ROWMIN(0) & ISC_PFE_CFG2_ROWMIN_MASK) |
+		     (ISC_PFE_CFG2_ROWMAX(h - 1) & ISC_PFE_CFG2_ROWMAX_MASK));
+
+	regmap_update_bits(regmap, ISC_PFE_CFG0,
+			   ISC_PFE_CFG0_COLEN | ISC_PFE_CFG0_ROWEN,
+			   ISC_PFE_CFG0_COLEN | ISC_PFE_CFG0_ROWEN);
 
 	addr0 = vb2_dma_contig_plane_dma_addr(&isc->cur_frm->vb.vb2_buf, 0);
 	regmap_write(regmap, ISC_DAD0, addr0);