gpu: ipu-v3: Fix dev_dbg frequency output

BugLink: https://bugs.launchpad.net/bugs/1969857
[ 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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/gpu/ipu-v3/ipu-di.c b/drivers/gpu/ipu-v3/ipu-di.c
index 666223c6bec4d52da44b38d3a0263f19bae2f4a6..0a34e0ab4fe60e7d4caad5d9c0272c3b4a391d05 100644 (file)
--- a/drivers/gpu/ipu-v3/ipu-di.c
+++ b/drivers/gpu/ipu-v3/ipu-di.c
@@ -447,8 +447,9 @@ 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) {