[RFC] drm/bridge: megachips-stdpxxxx-ge-b850v3-fw: switch to drm_do_get_edid()

[Jani Nikula]

The driver was originally added in commit fcfa0ddc18ed ("drm/bridge:
Drivers for megachips-stdpxxxx-ge-b850v3-fw (LVDS-DP++)"). I tried to
look up the discussion, but didn't find anyone questioning the EDID
reading part.

Why does it not use drm_get_edid() or drm_do_get_edid()?

I don't know where client->addr comes from, so I guess it could be
different from DDC_ADDR, rendering drm_get_edid() unusable.

There's also the comment:

	/* Yes, read the entire buffer, and do not skip the first
	 * EDID_LENGTH bytes.
	 */

But again, there's not a word on *why*.

Maybe we could just use drm_do_get_edid()? I'd like drivers to migrate
away from their own EDID parsing and validity checks, including stop
using drm_edid_block_valid(). (And long term switch to drm_edid_read(),
struct drm_edid, and friends, but this is the first step.)

Cc: Andrzej Hajda <andrzej.hajda at intel.com>
Cc: Ian Ray <ian.ray at ge.com>
Cc: Jernej Skrabec <jernej.skrabec at gmail.com>
Cc: Jonas Karlman <jonas at kwiboo.se>
Cc: Laurent Pinchart <Laurent.pinchart at ideasonboard.com>
Cc: Martin Donnelly <martin.donnelly at ge.com>
Cc: Martyn Welch <martyn.welch at collabora.co.uk>
Cc: Neil Armstrong <neil.armstrong at linaro.org>
Cc: Peter Senna Tschudin <peter.senna at gmail.com>
Cc: Robert Foss <rfoss at kernel.org>
Cc: Yuan Can <yuancan at huawei.com>
Cc: Zheyu Ma <zheyuma97 at gmail.com>
Signed-off-by: Jani Nikula <jani.nikula at intel.com>

---

I haven't even tried to compile this, and I have no way to test
this. Apologies for the long Cc list; I'm hoping someone could explain
the existing code, and perhaps give this approach a spin.
---
 .../bridge/megachips-stdpxxxx-ge-b850v3-fw.c  | 57 +++----------------
 1 file changed, 9 insertions(+), 48 deletions(-)

diff --git a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
index 460db3c8a08c..0d9eacf3d9b7 100644
--- a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
+++ b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
@@ -65,12 +65,11 @@ struct ge_b850v3_lvds {
 
 static struct ge_b850v3_lvds *ge_b850v3_lvds_ptr;
 
-static u8 *stdp2690_get_edid(struct i2c_client *client)
+static int stdp2690_read_block(void *context, u8 *buf, unsigned int block, size_t len)
 {
+	struct i2c_client *client = context;
 	struct i2c_adapter *adapter = client->adapter;
-	unsigned char start = 0x00;
-	unsigned int total_size;
-	u8 *block = kmalloc(EDID_LENGTH, GFP_KERNEL);
+	unsigned char start = block * EDID_LENGTH;
 
 	struct i2c_msg msgs[] = {
 		{
@@ -81,53 +80,15 @@ static u8 *stdp2690_get_edid(struct i2c_client *client)
 		}, {
 			.addr	= client->addr,
 			.flags	= I2C_M_RD,
-			.len	= EDID_LENGTH,
-			.buf	= block,
+			.len	= len,
+			.buf	= buf,
 		}
 	};
 
-	if (!block)
-		return NULL;
+	if (i2c_transfer(adapter, msgs, 2) != 2)
+		return -1;
 
-	if (i2c_transfer(adapter, msgs, 2) != 2) {
-		DRM_ERROR("Unable to read EDID.\n");
-		goto err;
-	}
-
-	if (!drm_edid_block_valid(block, 0, false, NULL)) {
-		DRM_ERROR("Invalid EDID data\n");
-		goto err;
-	}
-
-	total_size = (block[EDID_EXT_BLOCK_CNT] + 1) * EDID_LENGTH;
-	if (total_size > EDID_LENGTH) {
-		kfree(block);
-		block = kmalloc(total_size, GFP_KERNEL);
-		if (!block)
-			return NULL;
-
-		/* Yes, read the entire buffer, and do not skip the first
-		 * EDID_LENGTH bytes.
-		 */
-		start = 0x00;
-		msgs[1].len = total_size;
-		msgs[1].buf = block;
-
-		if (i2c_transfer(adapter, msgs, 2) != 2) {
-			DRM_ERROR("Unable to read EDID extension blocks.\n");
-			goto err;
-		}
-		if (!drm_edid_block_valid(block, 1, false, NULL)) {
-			DRM_ERROR("Invalid EDID data\n");
-			goto err;
-		}
-	}
-
-	return block;
-
-err:
-	kfree(block);
-	return NULL;
+	return 0;
 }
 
 static struct edid *ge_b850v3_lvds_get_edid(struct drm_bridge *bridge,
@@ -137,7 +98,7 @@ static struct edid *ge_b850v3_lvds_get_edid(struct drm_bridge *bridge,
 
 	client = ge_b850v3_lvds_ptr->stdp2690_i2c;
 
-	return (struct edid *)stdp2690_get_edid(client);
+	return drm_do_get_edid(connector, stdp2690_read_block, client, NULL);
 }
 
 static int ge_b850v3_lvds_get_modes(struct drm_connector *connector)
-- 
2.39.2