V4L/DVB (13179): gspca_ov519: cache sensor regs to avoid unnecessary slow i2c reads / writes

Cache sensor regs to avoid unnecessary slow i2c reads / writes, this speeds
up sd_start a bit with most bridges and a lot (from 5 seconds down to 0.3
seconds) with W996xCF cams, as this avoids very slow bit bang IO over
USB i2c reads.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 43 insertions, 10 deletions

diff --git a/drivers/media/video/gspca/ov519.c b/drivers/media/video/gspca/ov519.c
index 994a5e927d2d..91e9b23a3a01 100644
--- a/drivers/media/video/gspca/ov519.c
+++ b/drivers/media/video/gspca/ov519.c
@@ -103,6 +103,7 @@ struct sd {
         u8 sensor_addr;
         int sensor_width;
         int sensor_height;
+        int sensor_reg_cache[256];
 };
 
 /* Note this is a bit of a hack, but the w9968cf driver needs the code for all
@@ -2210,38 +2211,70 @@ static int ovfx2_i2c_r(struct sd *sd, __u8 reg)
 
 static int i2c_w(struct sd *sd, __u8 reg, __u8 value)
 {
+        int ret = -1;
+
+        if (sd->sensor_reg_cache[reg] == value)
+                return 0;
+
         switch (sd->bridge) {
         case BRIDGE_OV511:
         case BRIDGE_OV511PLUS:
-                return ov511_i2c_w(sd, reg, value);
+                ret = ov511_i2c_w(sd, reg, value);
+                break;
         case BRIDGE_OV518:
         case BRIDGE_OV518PLUS:
         case BRIDGE_OV519:
-                return ov518_i2c_w(sd, reg, value);
+                ret = ov518_i2c_w(sd, reg, value);
+                break;
         case BRIDGE_OVFX2:
-                return ovfx2_i2c_w(sd, reg, value);
+                ret = ovfx2_i2c_w(sd, reg, value);
+                break;
         case BRIDGE_W9968CF:
-                return w9968cf_i2c_w(sd, reg, value);
+                ret = w9968cf_i2c_w(sd, reg, value);
+                break;
+        }
+
+        if (ret >= 0) {
+                /* Up on sensor reset empty the register cache */
+                if (reg == 0x12 && (value & 0x80))
+                        memset(sd->sensor_reg_cache, -1,
+                               sizeof(sd->sensor_reg_cache));
+                else
+                        sd->sensor_reg_cache[reg] = value;
         }
-        return -1; /* Should never happen */
+
+        return ret;
 }
 
 static int i2c_r(struct sd *sd, __u8 reg)
 {
+        int ret;
+
+        if (sd->sensor_reg_cache[reg] != -1)
+                return sd->sensor_reg_cache[reg];
+
         switch (sd->bridge) {
         case BRIDGE_OV511:
         case BRIDGE_OV511PLUS:
-                return ov511_i2c_r(sd, reg);
+                ret = ov511_i2c_r(sd, reg);
+                break;
         case BRIDGE_OV518:
         case BRIDGE_OV518PLUS:
         case BRIDGE_OV519:
-                return ov518_i2c_r(sd, reg);
+                ret = ov518_i2c_r(sd, reg);
+                break;
         case BRIDGE_OVFX2:
-                return ovfx2_i2c_r(sd, reg);
+                ret = ovfx2_i2c_r(sd, reg);
+                break;
         case BRIDGE_W9968CF:
-                return w9968cf_i2c_r(sd, reg);
+                ret = w9968cf_i2c_r(sd, reg);
+                break;
         }
-        return -1; /* Should never happen */
+
+        if (ret >= 0)
+                sd->sensor_reg_cache[reg] = ret;
+
+        return ret;
 }
 
 /* Writes bits at positions specified by mask to an I2C reg. Bits that are in