[PATCH v2 2/3] drm/ast: Map fbdev framebuffer while it's being displayed

Thomas Zimmermann tzimmermann at suse.de
Wed Sep 4 11:56:43 UTC 2019

The generic fbdev emulation will map and unmap the framebuffer's memory
if required. As consoles are most often updated while being on screen,
we map the fbdev buffer while it's being displayed. This avoids frequent
map/unmap operations in the fbdev code. The original fbdev code in ast
used the same trick to improve performance.

	* fix typo in comment

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Cc: Noralf Trønnes <noralf at tronnes.org>
Cc: Dave Airlie <airlied at redhat.com>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Sam Ravnborg <sam at ravnborg.org>
Cc: Gerd Hoffmann <kraxel at redhat.com>
Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko at epam.com>
Cc: CK Hu <ck.hu at mediatek.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Alex Deucher <alexander.deucher at amd.com>
Cc: "Christian König" <christian.koenig at amd.com>
Cc: YueHaibing <yuehaibing at huawei.com>
Cc: Sam Bobroff <sbobroff at linux.ibm.com>
Cc: Huang Rui <ray.huang at amd.com>
Cc: "Y.C. Chen" <yc_chen at aspeedtech.com>
Cc: Rong Chen <rong.a.chen at intel.com>
Cc: Feng Tang <feng.tang at intel.com>
Cc: Huang Ying <ying.huang at intel.com>
Cc: Davidlohr Bueso <dave at stgolabs.net>
 drivers/gpu/drm/ast/ast_mode.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index d349c721501c..c10fff652228 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -529,13 +529,20 @@ static int ast_crtc_do_set_base(struct drm_crtc *crtc,
 				struct drm_framebuffer *fb,
 				int x, int y, int atomic)
+	struct drm_fb_helper *fb_helper = crtc->dev->fb_helper;
 	struct drm_gem_vram_object *gbo;
 	int ret;
 	s64 gpu_addr;
+	void *base;
 	if (!atomic && fb) {
 		gbo = drm_gem_vram_of_gem(fb->obj[0]);
+		// Unmap fbdev FB if it's not being displayed
+		// any longer.
+		if (fb == fb_helper->buffer->fb)
+			drm_gem_vram_kunmap(gbo);
 	gbo = drm_gem_vram_of_gem(crtc->primary->fb->obj[0]);
@@ -552,6 +559,14 @@ static int ast_crtc_do_set_base(struct drm_crtc *crtc,
 	ast_set_start_address_crt1(crtc, (u32)gpu_addr);
+	// Map fbdev FB while it's being displayed. This avoids frequent
+	// mapping and unmapping within the fbdev code.
+	if (crtc->primary->fb == fb_helper->buffer->fb) {
+		base = drm_gem_vram_kmap(gbo, true, NULL);
+		if (IS_ERR(base))
+			DRM_ERROR("failed to kmap fbcon\n");
+	}
 	return 0;
@@ -605,10 +620,14 @@ static void ast_crtc_disable(struct drm_crtc *crtc)
 	ast_crtc_dpms(crtc, DRM_MODE_DPMS_OFF);
 	if (crtc->primary->fb) {
+		struct drm_fb_helper *fb_helper = crtc->dev->fb_helper;
 		struct drm_framebuffer *fb = crtc->primary->fb;
 		struct drm_gem_vram_object *gbo =
+		// Unmap if it's the fbdev FB.
+		if (fb == fb_helper->buffer->fb)
+			drm_gem_vram_kunmap(gbo);
 	crtc->primary->fb = NULL;

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