[PATCH 4.9 209/218] gpu: ipu-v3: Fix dev_dbg frequency output

Greg Kroah-Hartman
2022-04-18T14:26:46Z

From: Leo Ruan <tingquan.ruan@cn.bosch.com>

[ Upstream commit 070a88fd4a03f921b73a2059e97d55faaa447dab ]

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>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Link: https://lore.kernel.org/r/20220207151411.5009-1-mark.jonas@de.bosch.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 a8d87ddd8a17..dc0511b22600 100644
--- a/drivers/gpu/ipu-v3/ipu-di.c
+++ b/drivers/gpu/ipu-v3/ipu-di.c
@@ -460,8 +460,9 @@ 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) {
--
2.35.1