We were previously selecting 1024x768 and 32BPP as the default
set-up for the PL111 consumers.
This does not work on elder systems: the device tree bindings
support a property "max-memory-bandwidth" in bytes/second that
states that if you exceed this the memory bus will saturate.
The result is flickering and unstable images.
Parse the "max-memory-bandwidth" and respect it when
intializing the driver. On the RealView PB11MP, Versatile and
Integrator/CP we get a nice console as default with this code.
Reviewed-by: Eric Anholt <eric@xxxxxxxxxx>
Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
---
ChangeLog v4->v5:
- Rebase on top of drm-next and resend so the patch
applies and produce a reasonable link. I have no clue
why patch does not apply, it looks like it should, but
the git moves in mysterious ways.
ChangeLog v3->v4:
- Switch the noisy DRM_INFO for DRM_DEBUG_KMS
- Collect Eric's review tag
ChangeLog v2->v3:
- Account for the case where there is no bandwidth limitation
so priv->memory_bw is zero. Then just accept any modes.
ChangeLog v1->v2:
- Exploit the new .mode_valid() callback we added to the
simple KMS helper.
- Use the hardcoded bits per pixel per variant instead of
trying to be heuristic about this setting for now.
---
drivers/gpu/drm/pl111/pl111_display.c | 36 +++++++++++++++++++++++++++++++++++
drivers/gpu/drm/pl111/pl111_drm.h | 1 +
drivers/gpu/drm/pl111/pl111_drv.c | 6 ++++++
3 files changed, 43 insertions(+)
diff --git a/drivers/gpu/drm/pl111/pl111_display.c b/drivers/gpu/drm/pl111/pl111_display.c
index 5b8368c76734..310646427907 100644
--- a/drivers/gpu/drm/pl111/pl111_display.c
+++ b/drivers/gpu/drm/pl111/pl111_display.c
@@ -50,6 +50,41 @@ irqreturn_t pl111_irq(int irq, void *data)
return status;
}
+static enum drm_mode_status
+pl111_mode_valid(struct drm_crtc *crtc,
+ const struct drm_display_mode *mode)
+{
+ struct drm_device *drm = crtc->dev;
+ struct pl111_drm_dev_private *priv = drm->dev_private;
+ u32 cpp = priv->variant->fb_bpp / 8;
+ u64 bw;
+
+ /*
+ * We use the pixelclock to also account for interlaced modes, the
+ * resulting bandwidth is in bytes per second.
+ */
+ bw = mode->clock * 1000; /* In Hz */
+ bw = bw * mode->hdisplay * mode->vdisplay * cpp;
+ bw = div_u64(bw, mode->htotal * mode->vtotal);
+
+ /*
+ * If no bandwidth constraints, anything goes, else
+ * check if we are too fast.
+ */
+ if (priv->memory_bw && (bw > priv->memory_bw)) {
+ DRM_DEBUG_KMS("%d x %d @ %d Hz, %d cpp, bw %llu too fast\n",
+ mode->hdisplay, mode->vdisplay,
+ mode->clock * 1000, cpp, bw);
+
+ return MODE_BAD;
+ }
+ DRM_DEBUG_KMS("%d x %d @ %d Hz, %d cpp, bw %llu bytes/s OK\n",
+ mode->hdisplay, mode->vdisplay,
+ mode->clock * 1000, cpp, bw);
+
+ return MODE_OK;
+}
+
static int pl111_display_check(struct drm_simple_display_pipe *pipe,
struct drm_plane_state *pstate,
struct drm_crtc_state *cstate)
@@ -348,6 +383,7 @@ static int pl111_display_prepare_fb(struct drm_simple_display_pipe *pipe,
}
static struct drm_simple_display_pipe_funcs pl111_display_funcs = {
+ .mode_valid = pl111_mode_valid,
.check = pl111_display_check,
.enable = pl111_display_enable,
.disable = pl111_display_disable,
diff --git a/drivers/gpu/drm/pl111/pl111_drm.h b/drivers/gpu/drm/pl111/pl111_drm.h
index 2a93e0134061..8639b2d4ddf7 100644
--- a/drivers/gpu/drm/pl111/pl111_drm.h
+++ b/drivers/gpu/drm/pl111/pl111_drm.h
@@ -65,6 +65,7 @@ struct pl111_drm_dev_private {
struct drm_simple_display_pipe pipe;
void *regs;
+ u32 memory_bw;
u32 ienb;
u32 ctrl;
/* The pixel clock (a reference to our clock divider off of CLCDCLK). */
diff --git a/drivers/gpu/drm/pl111/pl111_drv.c b/drivers/gpu/drm/pl111/pl111_drv.c
index e92a406c9ea9..4621259d5387 100644
--- a/drivers/gpu/drm/pl111/pl111_drv.c
+++ b/drivers/gpu/drm/pl111/pl111_drv.c
@@ -257,6 +257,12 @@ static int pl111_amba_probe(struct amba_device *amba_dev,
drm->dev_private = priv;
priv->variant = variant;
+ if (of_property_read_u32(dev->of_node, "max-memory-bandwidth",
+ &priv->memory_bw)) {
+ dev_info(dev, "no max memory bandwidth specified, assume unlimited\n");
+ priv->memory_bw = 0;
+ }
+
/* The two variants swap this register */
if (variant->is_pl110) {
priv->ienb = CLCD_PL110_IENB;
--
2.14.3
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