drm/i915: clarify that checking the FB stride for CFB is intentional

Daniel was looking at this code and asked about whether fb->pitches[0]
is correct, then he suggested we should a comment to make sure it is
actually intentional.

For more information on the CFB size calculation, please see the
commit message of:

commit c4ffd40908c30a33291227920e921f6b45b9e8f7
Author: Paulo Zanoni <paulo.r.zanoni@intel.com>
Date:   Thu Oct 1 19:55:57 2015 -0300
    drm/i915: fix CFB size calculation

Requested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1446664257-32012-12-git-send-email-paulo.r.zanoni@intel.com
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
index b015b09106454cec98f1c9e01aaea4c2dbf299de..4bd98025e535c253a3d6a8fcce55598ef6e413aa 100644 (file)
--- a/drivers/gpu/drm/i915/intel_fbc.c
+++ b/drivers/gpu/drm/i915/intel_fbc.c
@@ -707,6 +707,7 @@ static int intel_fbc_calculate_cfb_size(struct intel_crtc *crtc)
        if (INTEL_INFO(dev_priv)->gen >= 7)
                lines = min(lines, 2048);
 
+       /* Hardware needs the full buffer stride, not just the active area. */
        return lines * fb->pitches[0];
 }