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Commit 936598d1 authored by Chen-Yu Tsai's avatar Chen-Yu Tsai Committed by Maxime Ripard
Browse files

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: default avatarChen-Yu Tsai <wens@csie.org>
Signed-off-by: default avatarMaxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171014040252.9621-5-wens@csie.org
parent cff2192f

drivers/gpu/drm/sun4i/sun4i_backend.c

+8 −1
Original line number Diff line number Diff line
@@ -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);