Unverified Commit 82a1356a authored by Samuel Holland's avatar Samuel Holland Committed by Maxime Ripard
Browse files

drm/sun4i: dsi: Prevent underflow when computing packet sizes 



Currently, the packet overhead is subtracted using unsigned arithmetic.
With a short sync pulse, this could underflow and wrap around to near
the maximal u16 value. Fix this by using signed subtraction. The call to
max() will correctly handle any negative numbers that are produced.

Apply the same fix to the other timings, even though those subtractions
are less likely to underflow.

Fixes: 133add5b ("drm/sun4i: Add Allwinner A31 MIPI-DSI controller support")
Signed-off-by: default avatarSamuel Holland <samuel@sholland.org>
Reviewed-by: default avatarJernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: default avatarMaxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220812031623.34057-1-samuel@sholland.org
parent 2a29f80e

drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c

+5 −5
Original line number Diff line number Diff line
@@ -531,7 +531,7 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi, 
				    struct drm_display_mode *mode)

{

	struct mipi_dsi_device *device = dsi->device;

	unsigned int Bpp = mipi_dsi_pixel_format_to_bpp(device->format) / 8;

	int Bpp = mipi_dsi_pixel_format_to_bpp(device->format) / 8;

	u16 hbp = 0, hfp = 0, hsa = 0, hblk = 0, vblk = 0;

	u32 basic_ctl = 0;

	size_t bytes;
@@ -555,7 +555,7 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi, 
		 * (4 bytes). Its minimal size is therefore 10 bytes

		 */

#define HSA_PACKET_OVERHEAD	10

		hsa = max((unsigned int)HSA_PACKET_OVERHEAD,

		hsa = max(HSA_PACKET_OVERHEAD,

			  (mode->hsync_end - mode->hsync_start) * Bpp - HSA_PACKET_OVERHEAD);



		/*
@@ -564,7 +564,7 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi, 
		 * therefore 6 bytes

		 */

#define HBP_PACKET_OVERHEAD	6

		hbp = max((unsigned int)HBP_PACKET_OVERHEAD,

		hbp = max(HBP_PACKET_OVERHEAD,

			  (mode->htotal - mode->hsync_end) * Bpp - HBP_PACKET_OVERHEAD);



		/*
@@ -574,7 +574,7 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi, 
		 * 16 bytes

		 */

#define HFP_PACKET_OVERHEAD	16

		hfp = max((unsigned int)HFP_PACKET_OVERHEAD,

		hfp = max(HFP_PACKET_OVERHEAD,

			  (mode->hsync_start - mode->hdisplay) * Bpp - HFP_PACKET_OVERHEAD);



		/*
@@ -583,7 +583,7 @@ static void sun6i_dsi_setup_timings(struct sun6i_dsi *dsi, 
		 * bytes). Its minimal size is therefore 10 bytes.

		 */

#define HBLK_PACKET_OVERHEAD	10

		hblk = max((unsigned int)HBLK_PACKET_OVERHEAD,

		hblk = max(HBLK_PACKET_OVERHEAD,

			   (mode->htotal - (mode->hsync_end - mode->hsync_start)) * Bpp -

			   HBLK_PACKET_OVERHEAD);