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drm/pl111: Use max memory bandwidth for resolution

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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@anholt.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180307215819.15814-1-linus.walleij@linaro.org
This commit is contained in:
Linus Walleij 2018-03-07 22:58:19 +01:00
parent 2e7a66a8b5
commit df99dd9202
3 changed files with 43 additions and 0 deletions
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36
drivers/gpu/drm/pl111/pl111_display.c
View File

@ -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,

1
drivers/gpu/drm/pl111/pl111_drm.h
View File

@ -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). */

6
drivers/gpu/drm/pl111/pl111_drv.c
View File

@ -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;