drm/i915: Read ilk FDI PLL frequency once during initialisation

During intel_atomic_check(), we do not take the intel_runtime_pm_get()
wakeref and so should do the atomic modeset precalculations without
referring to the HW. However, on Ironlake we see

<7>[   23.487557] [drm:intel_atomic_check [i915]] [CONNECTOR:47:VGA-1] checking for sink bpp constrains
<7>[   23.487615] [drm:intel_atomic_check [i915]] clamping display bpp (was 36) to default limit of 24
<4>[   23.487621] RPM wakelock ref not held during HW access
<4>[   23.487652] ------------[ cut here ]------------
<4>[   23.487697] WARNING: CPU: 0 PID: 1343 at drivers/gpu/drm/i915/intel_drv.h:1813 gen5_read32+0x183/0x200 [i915]
<4>[   23.487701] Modules linked in: snd_hda_codec_hdmi snd_hda_codec_realtek snd_hda_codec_generic i915 intel_powerclamp coretemp crct10dif_pclmul crc32_pclmul snd_hda_intel ghash_clmulni_intel snd_hda_codec snd_hwdep snd_hda_core snd_pcm lpc_ich e1000e mei_me ptp mei pps_core prime_numbers
<4>[   23.487784] CPU: 0 PID: 1343 Comm: debugfs_test Tainted: G        W       4.14.0-rc7-CI-Trybot_1378+ #1
<4>[   23.487788] Hardware name: Hewlett-Packard HP Compaq 8100 Elite SFF PC/304Ah, BIOS 786H1 v01.13 07/14/2011
<4>[   23.487793] task: ffff8801f90aa6c0 task.stack: ffffc900013ec000
<4>[   23.487838] RIP: 0010:gen5_read32+0x183/0x200 [i915]
<4>[   23.487842] RSP: 0018:ffffc900013efb58 EFLAGS: 00010292
<4>[   23.487849] RAX: 000000000000002a RBX: ffff880205c00000 RCX: 0000000000000006
<4>[   23.487854] RDX: 000000000000140a RSI: ffffffff81d0eb14 RDI: ffffffff81cc26f6
<4>[   23.487857] RBP: ffffc900013efb80 R08: ffff8801f90aaff8 R09: 0000000000000000
<4>[   23.487861] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
<4>[   23.487865] R13: 0000000000046000 R14: ffff88020ffaba78 R15: ffff88020b109bf8
<4>[   23.487870] FS:  00007f53b5e40a40(0000) GS:ffff88021bc00000(0000) knlGS:0000000000000000
<4>[   23.487874] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4>[   23.487878] CR2: 000055e41900c0e8 CR3: 00000001fa0d6005 CR4: 00000000000206f0
<4>[   23.487882] Call Trace:
<4>[   23.487931]  intel_atomic_check+0x745/0x1290 [i915]
<4>[   23.487948]  drm_atomic_check_only+0x459/0x560
<4>[   23.487956]  ? drm_atomic_set_crtc_for_connector+0xc9/0x100
<4>[   23.488025]  drm_atomic_commit+0x18/0x50
<4>[   23.488035]  restore_fbdev_mode_atomic+0x190/0x1f0
<4>[   23.488059]  restore_fbdev_mode+0x32/0x120
<4>[   23.488072]  drm_fb_helper_restore_fbdev_mode_unlocked+0x50/0xa0
<4>[   23.488139]  intel_fbdev_restore_mode+0x34/0x90 [i915]
<4>[   23.488194]  i915_driver_lastclose+0xe/0x10 [i915]
<4>[   23.488208]  drm_lastclose+0x39/0xf0
<4>[   23.488219]  drm_release+0x30c/0x3c0
<4>[   23.488236]  __fput+0xb9/0x200
<4>[   23.488252]  ____fput+0xe/0x10
<4>[   23.488264]  task_work_run+0x89/0xc0
<4>[   23.488278]  exit_to_usermode_loop+0x83/0x90
<4>[   23.488290]  syscall_return_slowpath+0xd0/0x110
<4>[   23.488304]  entry_SYSCALL_64_fastpath+0xaf/0xb1
<4>[   23.488312] RIP: 0033:0x7f53b4317560
<4>[   23.488320] RSP: 002b:00007ffca7e70748 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
<4>[   23.488333] RAX: 0000000000000000 RBX: 0000000000000001 RCX: 00007f53b4317560
<4>[   23.488340] RDX: 0000000000000005 RSI: 00007ffca7e70640 RDI: 0000000000000004
<4>[   23.488347] RBP: 000055e417783900 R08: 000055e418f9e290 R09: 0000000000000000
<4>[   23.488356] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
<4>[   23.488363] R13: 00007f53b4302c40 R14: 0000000000000000 R15: 0000000000000000
<4>[   23.488384] Code: b5 f2 f2 e0 0f ff e9 c5 fe ff ff 80 3d 0e 4b 10 00 00 0f 85 c6 fe ff ff 48 c7 c7 30 73 29 a0 c6 05 fa 4a 10 00 01 e8 8e f2 f2 e0 <0f> ff e9 ac fe ff ff e8 51 9d f3 e0 85 c0 0f 85 01 ff ff ff 48
<4>[   23.488780] ---[ end trace 6bc72ce7f1596190 ]---
<7>[   23.488844] [drm:intel_atomic_check [i915]] checking fdi config on pipe A, lanes 1
<7>[   23.488911] [drm:intel_atomic_check [i915]] hw max bpp: 36, pipe bpp: 24, dithering: 0

due to intel_fdi_link_freq() poking at FDI_PLL_BIOS_0. Avoid this by
recording the fdi pll frequency during device initiailisation.

v2: Also extract the static FDI PLL frequencies for Sandybridge and
Ivybridge.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171107214713.18704-1-chris@chris-wilson.co.uk
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

drivers/gpu/drm/i915/i915_drv.h

@@ -2349,6 +2349,7 @@ struct drm_i915_private {
 	unsigned int max_dotclk_freq;
 	unsigned int rawclk_freq;
 	unsigned int hpll_freq;
+	unsigned int fdi_pll_freq;
 	unsigned int czclk_freq;
 
 	struct {

drivers/gpu/drm/i915/intel_display.c

@@ -219,10 +219,8 @@ intel_fdi_link_freq(struct drm_i915_private *dev_priv,
 {
 	if (HAS_DDI(dev_priv))
 		return pipe_config->port_clock; /* SPLL */
-	else if (IS_GEN5(dev_priv))
-		return ((I915_READ(FDI_PLL_BIOS_0) & FDI_PLL_FB_CLOCK_MASK) + 2) * 10000;
 	else
-		return 270000;
+		return dev_priv->fdi_pll_freq;
 }
 
 static const struct intel_limit intel_limits_i8xx_dac = {
@@ -14454,6 +14452,22 @@ fail:
 	drm_modeset_acquire_fini(&ctx);
 }
 
+static void intel_update_fdi_pll_freq(struct drm_i915_private *dev_priv)
+{
+	if (IS_GEN5(dev_priv)) {
+		u32 fdi_pll_clk =
+			I915_READ(FDI_PLL_BIOS_0) & FDI_PLL_FB_CLOCK_MASK;
+
+		dev_priv->fdi_pll_freq = (fdi_pll_clk + 2) * 10000;
+	} else if (IS_GEN6(dev_priv) || IS_IVYBRIDGE(dev_priv)) {
+		dev_priv->fdi_pll_freq = 270000;
+	} else {
+		return;
+	}
+
+	DRM_DEBUG_DRIVER("FDI PLL freq=%d\n", dev_priv->fdi_pll_freq);
+}
+
 int intel_modeset_init(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
@@ -14541,6 +14555,7 @@ int intel_modeset_init(struct drm_device *dev)
 	}
 
 	intel_shared_dpll_init(dev);
+	intel_update_fdi_pll_freq(dev_priv);
 
 	intel_update_czclk(dev_priv);
 	intel_modeset_init_hw(dev);