diff options
| author | Chen-Yu Tsai <wens@csie.org> | 2017-10-14 12:02:49 +0800 |
|---|---|---|
| committer | Maxime Ripard <maxime.ripard@free-electrons.com> | 2017-10-16 09:54:01 +0200 |
| commit | 936598d16e9111e3802d45a60c028ad36a3a7013 (patch) | |
| tree | 2b318379b24c30e1e794cd45b0b494a4098be38d /drivers/gpu/drm | |
| parent | cff2192f807d442e498d43a20e54c6851cd4cb56 (diff) | |
drm/sun4i: backend: Add comment explaining why registers are cleared
Many of the backend's layer configuration registers have undefined
default values. This poses a risk as we use regmap_update_bits in
some places, and don't overwrite the whole register.
At probe/bind time we explicitly clear all the control registers
by writing 0 to them. This patch adds a more detailed explanation
on why we're doing this.
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171014040252.9621-5-wens@csie.org
Diffstat (limited to 'drivers/gpu/drm')
| -rw-r--r-- | drivers/gpu/drm/sun4i/sun4i_backend.c | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c index 243ddfdc9403..4fefd8add714 100644 --- a/drivers/gpu/drm/sun4i/sun4i_backend.c +++ b/drivers/gpu/drm/sun4i/sun4i_backend.c @@ -412,7 +412,14 @@ static int sun4i_backend_bind(struct device *dev, struct device *master, list_add_tail(&backend->engine.list, &drv->engine_list); - /* Reset the registers */ + /* + * Many of the backend's layer configuration registers have + * undefined default values. This poses a risk as we use + * regmap_update_bits in some places, and don't overwrite + * the whole register. + * + * Clear the registers here to have something predictable. + */ for (i = 0x800; i < 0x1000; i += 4) regmap_write(backend->engine.regs, i, 0); |