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From:   Mark Jonas <mark.jonas@de.bosch.com>
To:     Philipp Zabel <p.zabel@pengutronix.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>
CC:     <dri-devel@lists.freedesktop.org>, <linux-kernel@vger.kernel.org>,
        <tingquan.ruan@cn.bosch.com>, <mark.jonas@de.bosch.com>
Subject: [PATCH] gpu: ipu-v3: Fix dev_dbg frequency output
Date:   Mon, 7 Feb 2022 16:14:11 +0100
Message-ID: <20220207151411.5009-1-mark.jonas@de.bosch.com>
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From: Leo Ruan <tingquan.ruan@cn.bosch.com>

This commit corrects the printing of the IPU clock error percentage if
it is between -0.1% to -0.9%. For example, if the pixel clock requested
is 27.2 MHz but only 27.0 MHz can be achieved the deviation is -0.8%.
But the fixed point math had a flaw and calculated error of 0.2%.

Before:
  Clocks: IPU 270000000Hz DI 24716667Hz Needed 27200000Hz
  IPU clock can give 27000000 with divider 10, error 0.2%
  Want 27200000Hz IPU 270000000Hz DI 24716667Hz using IPU, 27000000Hz

After:
  Clocks: IPU 270000000Hz DI 24716667Hz Needed 27200000Hz
  IPU clock can give 27000000 with divider 10, error -0.8%
  Want 27200000Hz IPU 270000000Hz DI 24716667Hz using IPU, 27000000Hz

Signed-off-by: Leo Ruan <tingquan.ruan@cn.bosch.com>
Signed-off-by: Mark Jonas <mark.jonas@de.bosch.com>
---
 drivers/gpu/ipu-v3/ipu-di.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/ipu-v3/ipu-di.c b/drivers/gpu/ipu-v3/ipu-di.c
index b4a31d506fcc..74eca68891ad 100644
--- a/drivers/gpu/ipu-v3/ipu-di.c
+++ b/drivers/gpu/ipu-v3/ipu-di.c
@@ -451,8 +451,9 @@ static void ipu_di_config_clock(struct ipu_di *di,
 
 		error = rate / (sig->mode.pixelclock / 1000);
 
-		dev_dbg(di->ipu->dev, "  IPU clock can give %lu with divider %u, error %d.%u%%\n",
-			rate, div, (signed)(error - 1000) / 10, error % 10);
+		dev_dbg(di->ipu->dev, "  IPU clock can give %lu with divider %u, error %c%d.%d%%\n",
+			rate, div, error < 1000 ? '-' : '+',
+			abs(error - 1000) / 10, abs(error - 1000) % 10);
 
 		/* Allow a 1% error */
 		if (error < 1010 && error >= 990) {
-- 
2.17.1