[PATCH v2] drm: Add drm_mode_num_active_pixels helper function

[Jonathan Cavitt]

Add a helper function that computes the product of hdisplay and
vdisplay.  This is necessary to prevent a potential sign extension
issue.

v2:
- Clarify purpose of helper function (Jonathan)
- s/drm_mode_display_size/drm_mode_num_active_pixels (Ville)
- Add kernel docs (Jani)

Signed-off-by: Jonathan Cavitt <jonathan.cav...@intel.com>
Cc: Matthew Auld <matthew.a...@intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimi...@intel.com>
Cc: Matthew Brost <matthew.br...@intel.com>
Cc: Ville Syrjälä <ville.syrj...@linux.intel.com>
Cc: Jani Nikula <jani.nik...@linux.intel.com>
---
 drivers/gpu/drm/drm_gem_vram_helper.c |  2 +-
 drivers/gpu/drm/drm_mipi_dbi.c        |  2 +-
 include/drm/drm_modes.h               | 14 ++++++++++++++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c 
b/drivers/gpu/drm/drm_gem_vram_helper.c
index 90760d0ca071..a345dc8caa3b 100644
--- a/drivers/gpu/drm/drm_gem_vram_helper.c
+++ b/drivers/gpu/drm/drm_gem_vram_helper.c
@@ -967,7 +967,7 @@ drm_vram_helper_mode_valid_internal(struct drm_device *dev,
 
        max_fbpages = (vmm->vram_size / 2) >> PAGE_SHIFT;
 
-       fbsize = mode->hdisplay * mode->vdisplay * max_bpp;
+       fbsize = drm_mode_num_active_pixels(mode) * max_bpp;
        fbpages = DIV_ROUND_UP(fbsize, PAGE_SIZE);
 
        if (fbpages > max_fbpages)
diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
index e33c78fc8fbd..08da48bfff36 100644
--- a/drivers/gpu/drm/drm_mipi_dbi.c
+++ b/drivers/gpu/drm/drm_mipi_dbi.c
@@ -691,7 +691,7 @@ int mipi_dbi_dev_init(struct mipi_dbi_dev *dbidev,
                      const struct drm_simple_display_pipe_funcs *funcs,
                      const struct drm_display_mode *mode, unsigned int 
rotation)
 {
-       size_t bufsize = mode->vdisplay * mode->hdisplay * sizeof(u16);
+       size_t bufsize = drm_mode_num_active_pixels(mode) * sizeof(u16);
 
        dbidev->drm.mode_config.preferred_depth = 16;
 
diff --git a/include/drm/drm_modes.h b/include/drm/drm_modes.h
index b9bb92e4b029..c0e8d6c4d43c 100644
--- a/include/drm/drm_modes.h
+++ b/include/drm/drm_modes.h
@@ -572,4 +572,18 @@ struct drm_display_mode *
 drm_mode_create_from_cmdline_mode(struct drm_device *dev,
                                  struct drm_cmdline_mode *cmd);
 
+/**
+ * drm_mode_num_active_pixels - Computes the number of pixels in the
+ * drm display mode
+ *
+ * @mode - The target drm_display_mode
+ *
+ * Returns the product of hdisplay and vdisplay
+ */
+static inline u32
+drm_mode_num_active_pixels(const struct drm_display_mode *mode)
+{
+       return mode->hdisplay * mode->vdisplay;
+}
+
 #endif /* __DRM_MODES_H__ */
-- 
2.43.0