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 --- 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 d75923896609..72e85397611a 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) @@ -344,6 +379,7 @@ static int pl111_display_prepare_fb(struct drm_simple_display_pipe *pipe, }
static const 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 360fbdd2203c..70b092670c04 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 73d252351438..b469aa317d9d 100644 --- a/drivers/gpu/drm/pl111/pl111_drv.c +++ b/drivers/gpu/drm/pl111/pl111_drv.c @@ -262,6 +262,12 @@ 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;