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video: udlfb: Fix unaligned access

PATCH In review Ladislav Michl 2 participants 4 messages Feb 6, 2018 – Mar 12, 2018

Subsystems (2)
Framebuffer layer Displaylink USB 2.0 framebuffer driver (udlfb)
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Ladislav Michl

author
#0 lore raw

PATCH 1/2 video: udlfb: Fix unaligned access

Driver generates lots of alignment trap exceptions on ARM. Fix that by replacing typecasting of odd addresses with byte shifting and remove uneccessary typecasting.

Signed-off-by Ladislav Michl <[email protected]>

---
Here's what happens on at91sam9g20 few minutes after boot:

 $ cat /proc/cpu/alignment
 User:           0
 System:         10747836 (dlfb_render_hline+0x22c/0x2f0 [udlfb])
 Skipped:        0
 Half:           10747971
 Word:           159
 DWord:          0
 Multi:          0
 Each hline transfer causes dozens alignment exceptions and
 few are in dlfb_parse_vendor_descriptor function.
 drivers/video/fbdev/udlfb.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)
drivers/video/fbdev/udlfb.c +12 -11
index 452a4207ac1b..45081297efa5 100644
@@ -441,9 +441,9 @@ static void dlfb_compress_hline(
 
 		*cmd++ = 0xAF;
 		*cmd++ = 0x6B;
-		*cmd++ = (uint8_t) ((dev_addr >> 16) & 0xFF);
-		*cmd++ = (uint8_t) ((dev_addr >> 8) & 0xFF);
-		*cmd++ = (uint8_t) ((dev_addr) & 0xFF);
+		*cmd++ = dev_addr >> 16;
+		*cmd++ = dev_addr >> 8;
+		*cmd++ = dev_addr;
 
 		cmd_pixels_count_byte = cmd++; /*  we'll know this later */
 		cmd_pixel_start = pixel;

@@ -460,8 +460,8 @@ static void dlfb_compress_hline(
 		while (pixel < cmd_pixel_end) {
 			const uint16_t * const repeating_pixel = pixel;
 
-			*(uint16_t *)cmd = cpu_to_be16p(pixel);
-			cmd += 2;
+			*cmd++ = *pixel >> 8;
+			*cmd++ = *pixel;
 			pixel++;
 
 			if (unlikely((pixel < cmd_pixel_end) &&

@@ -1531,15 +1531,16 @@ static int dlfb_parse_vendor_descriptor(struct dlfb_data *dlfb,
 			u8 length;
 			u16 key;
 
-			key = le16_to_cpu(*((u16 *) desc));
-			desc += sizeof(u16);
-			length = *desc;
-			desc++;
+			key = *desc++;
+			key |= (u16)*desc++ << 8;
+			length = *desc++;
 
 			switch (key) {
 			case 0x0200: { /* max_area */
-				u32 max_area;
-				max_area = le32_to_cpu(*((u32 *)desc));
+				u32 max_area = *desc++;
+				max_area |= (u32)*desc++ << 8;
+				max_area |= (u32)*desc++ << 16;
+				max_area |= (u32)*desc++ << 24;
 				dev_warn(&intf->dev,
 					 "DL chip limited to %d pixel modes\n",
 					 max_area);
Signature · 1 line
2.16.1
#1 lore raw
Quoted 5 lines · Ladislav Michl

Driver generates lots of alignment trap exceptions on ARM. Fix that by replacing typecasting of odd addresses with byte shifting and remove uneccessary typecasting.

Signed-off-by Ladislav Michl <[email protected]>

Patch queued for 4.17, thanks.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

author
#2 lore raw

PATCH 2/2 video: udlfb: Use already defined BPP constant

Replace const variable with already defined constant.

Signed-off-by Ladislav Michl <[email protected]>
---
 drivers/video/fbdev/udlfb.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)
drivers/video/fbdev/udlfb.c +3 -4
index 45081297efa5..7b53fefb4b94 100644
@@ -428,7 +428,6 @@ static void dlfb_compress_hline(
 	const uint16_t *pixel = *pixel_start_ptr;
 	uint32_t dev_addr  = *device_address_ptr;
 	uint8_t *cmd = *command_buffer_ptr;
-	const int bpp = 2;
 
 	while ((pixel_end > pixel) &&
 	       (cmd_buffer_end - MIN_RLX_CMD_BYTES > cmd)) {

@@ -453,9 +452,9 @@ static void dlfb_compress_hline(
 
 		cmd_pixel_end = pixel + min(MAX_CMD_PIXELS + 1,
 			min((int)(pixel_end - pixel),
-			    (int)(cmd_buffer_end - cmd) / bpp));
+			    (int)(cmd_buffer_end - cmd) / BPP));
 
-		prefetch_range((void *) pixel, (cmd_pixel_end - pixel) * bpp);
+		prefetch_range((void *) pixel, (cmd_pixel_end - pixel) * BPP);
 
 		while (pixel < cmd_pixel_end) {
 			const uint16_t * const repeating_pixel = pixel;

@@ -490,7 +489,7 @@ static void dlfb_compress_hline(
 		}
 
 		*cmd_pixels_count_byte = (pixel - cmd_pixel_start) & 0xFF;
-		dev_addr += (pixel - cmd_pixel_start) * bpp;
+		dev_addr += (pixel - cmd_pixel_start) * BPP;
 	}
 
 	if (cmd_buffer_end <= MIN_RLX_CMD_BYTES + cmd) {
Signature · 1 line
2.16.1
#3 lore raw

Re: [PATCH 2/2] video: udlfb: Use already defined BPP constant

Quoted 3 lines · Ladislav Michl

Replace const variable with already defined constant.

Signed-off-by Ladislav Michl <[email protected]>

Patch queued for 4.17, thanks.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics