linux-kernel - [PATCH v3 12/12] media: i2c: imx214: Fix link frequency

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Message-Id: <20241207-imx214-v3-12-ab60af7ee915@apitzsch.eu>
Date: Sat, 07 Dec 2024 21:48:01 +0100
From: André Apitzsch via B4 Relay <devnull+git.apitzsch.eu@...nel.org>
To: Ricardo Ribalda <ribalda@...nel.org>, 
 Sakari Ailus <sakari.ailus@...ux.intel.com>, 
 Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org, 
 linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Dave Stevenson <dave.stevenson@...pberrypi.com>, 
 Vincent Knecht <vincent.knecht@...loo.org>, 
 André Apitzsch <git@...tzsch.eu>
Subject: [PATCH v3 12/12] media: i2c: imx214: Fix link frequency

From: André Apitzsch <git@...tzsch.eu>

The driver defines IMX214_DEFAULT_LINK_FREQ 480000000, and then
IMX214_DEFAULT_PIXEL_RATE ((IMX214_DEFAULT_LINK_FREQ * 8LL) / 10),
which works out as 384MPix/s. (The 8 is 4 lanes and DDR.)

Parsing the PLL registers with the defined 24MHz input. We're in single
PLL mode, so MIPI frequency is directly linked to pixel rate.  VTCK ends
up being 1200MHz, and VTPXCK and OPPXCK both are 120MHz.  Section 5.3
"Frame rate calculation formula" says "Pixel rate
[pixels/s] = VTPXCK [MHz] * 4", so 120 * 4 = 480MPix/s, which basically
agrees with my number above.

3.1.4. MIPI global timing setting says "Output bitrate = OPPXCK * reg
0x113[7:0]", so 120MHz * 10, or 1200Mbit/s. That would be a link
frequency of 600MHz due to DDR.
That also matches to 480MPix/s * 10bpp / 4 lanes / 2 for DDR.

Keep the previous link frequency for backward compatibility.

Signed-off-by: André Apitzsch <git@...tzsch.eu>
---
 drivers/media/i2c/imx214.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/media/i2c/imx214.c b/drivers/media/i2c/imx214.c
index 1330f13207beec0960c384681bf0b49e99fe860f..910ad03cda23345d3d10d13cd30f007954534e80 100644
--- a/drivers/media/i2c/imx214.c
+++ b/drivers/media/i2c/imx214.c
@@ -31,7 +31,9 @@
 #define IMX214_REG_FAST_STANDBY_CTRL	CCI_REG8(0x0106)
 
 #define IMX214_DEFAULT_CLK_FREQ	24000000
-#define IMX214_DEFAULT_LINK_FREQ 480000000
+#define IMX214_DEFAULT_LINK_FREQ	600000000
+/* Keep wrong link frequency for backward compatibility */
+#define IMX214_DEFAULT_LINK_FREQ_LEGACY	480000000
 #define IMX214_DEFAULT_PIXEL_RATE ((IMX214_DEFAULT_LINK_FREQ * 8LL) / 10)
 #define IMX214_FPS 30
 
@@ -1216,18 +1218,22 @@ static int imx214_parse_fwnode(struct device *dev)
 		goto done;
 	}
 
-	for (i = 0; i < bus_cfg.nr_of_link_frequencies; i++)
+	for (i = 0; i < bus_cfg.nr_of_link_frequencies; i++) {
 		if (bus_cfg.link_frequencies[i] == IMX214_DEFAULT_LINK_FREQ)
 			break;
-
-	if (i == bus_cfg.nr_of_link_frequencies) {
-		dev_err_probe(dev, -EINVAL,
-			      "link-frequencies %d not supported, Please review your DT\n",
-			      IMX214_DEFAULT_LINK_FREQ);
-		ret = -EINVAL;
-		goto done;
+		if (bus_cfg.link_frequencies[i] == IMX214_DEFAULT_LINK_FREQ_LEGACY) {
+			dev_warn(dev,
+				 "link-frequencies %d not supported, please review your DT. Continuing anyway\n",
+				 IMX214_DEFAULT_LINK_FREQ);
+			break;
+		}
 	}
 
+	if (i == bus_cfg.nr_of_link_frequencies)
+		ret = dev_err_probe(dev, -EINVAL,
+				    "link-frequencies %d not supported, please review your DT\n",
+				    IMX214_DEFAULT_LINK_FREQ);
+
 done:
 	v4l2_fwnode_endpoint_free(&bus_cfg);
 	fwnode_handle_put(endpoint);

-- 
2.47.1