i915: fix build on gcc7

With gcc7, the conditional usage of (port == PORT_A ? PORT_C : PORT_A) triggers -Werror=int-in-bool-context which breaks the build. Instead, use a temporary port_other variable that avoids hitting this error.

% gcc --version
gcc (SUSE Linux) 7.1.1 20170517 [gcc-7-branch revision 248152]
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
% make -j8 drivers/gpu/drm/i915/intel_dsi.o
In file included from drivers/gpu/drm/i915/intel_dsi.c:34:0:
drivers/gpu/drm/i915/intel_dsi.c: In function ‘intel_dsi_prepare’:
drivers/gpu/drm/i915/intel_dsi.c:1487:23: error: ?: using integer constants in boolean context [-Werror=int-in-bool-context]

         PORT_A ? PORT_C : PORT_A),
  drivers/gpu/drm/i915/i915_drv.h:3909:76: note: in definition of macro ‘I915_WRITE’
   #define I915_WRITE(reg, val) dev_priv->uncore.funcs.mmio_writel(dev_priv, (reg), (val), true)
                                                                              ^~~
  drivers/gpu/drm/i915/i915_reg.h:8280:32: note: in expansion of macro ‘_MMIO’
   #define _MMIO_MIPI(port, a, c) _MMIO(_MIPI_PORT(port, a, c))
                                  ^~~~~
  drivers/gpu/drm/i915/i915_reg.h:8280:38: note: in expansion of macro ‘_MIPI_PORT’
   #define _MMIO_MIPI(port, a, c) _MMIO(_MIPI_PORT(port, a, c))
                                        ^~~~~~~~~~
  drivers/gpu/drm/i915/i915_reg.h:8624:32: note: in expansion of macro ‘_MMIO_MIPI’
   #define MIPI_INIT_COUNT(port)  _MMIO_MIPI(port, _MIPIA_INIT_COUNT, _MIPIC_INIT_COUNT)
                                  ^~~~~~~~~~
  drivers/gpu/drm/i915/intel_dsi.c:1486:15: note: in expansion of macro ‘MIPI_INIT_COUNT’
      I915_WRITE(MIPI_INIT_COUNT(port ==
                 ^~~~~~~~~~~~~~~

Signed-off-by Aleksa Sarai <[email protected]>

---
 drivers/gpu/drm/i915/intel_dsi.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

drivers/gpu/drm/i915/intel_dsi.c +3 -2

index 54030b68406a..53e717e7b811 100644
@@ -1476,14 +1476,15 @@ static void intel_dsi_prepare(struct intel_encoder *intel_encoder,
 				txclkesc(intel_dsi->escape_clk_div, 100));
 
 		if (IS_GEN9_LP(dev_priv) && (!intel_dsi->dual_link)) {
+			enum port port_other = port == PORT_A ? PORT_C : PORT_A;
+
 			/*
 			 * BXT spec says write MIPI_INIT_COUNT for
 			 * both the ports, even if only one is
 			 * getting used. So write the other port
 			 * if not in dual link mode.
 			 */
-			I915_WRITE(MIPI_INIT_COUNT(port ==
-						PORT_A ? PORT_C : PORT_A),
+			I915_WRITE(MIPI_INIT_COUNT(port_other),
 					intel_dsi->init_count);
 		}

This is probably already fixed in drm-next by

commit 0ad4dc887d4168448e8c801aa4edd8fe1e0bd534

Author: Hans de Goede <[email protected]>
Date:   Thu May 18 13:06:44 2017 +0200

drm/i915: Fix new -Wint-in-bool-context gcc compiler warning

Quoted 1 line

which I also think is a more sensible fix than this one.