Because of its shallow queues and limited reordering ability, the i.MX6Q memory controller likes AXI bursts of consecutive addresses a lot. To optimize memory access performance, lock the IPU scanout channels for a number of burst accesses each, before switching to the next channel. The burst size and length of a locked burst chain are chosen not to overshoot the stride.
Enabling the 8-burst channel lock on a single 1920x1080@60Hz RGBx scanout (474 MiB/s of 64-byte IPU memory read accesses) reduces the reported memory controller busy cycles from 46% to below 28% on an otherwise idle i.MX6Q.
Tested-by: Lucas Stach l.stach@pengutronix.de Signed-off-by: Philipp Zabel p.zabel@pengutronix.de --- drivers/gpu/drm/imx/ipuv3-plane.c | 38 +++++++++++++++++++++++++++++++++++--- 1 file changed, 35 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/imx/ipuv3-plane.c b/drivers/gpu/drm/imx/ipuv3-plane.c index a9292e3d3c437..46e7e44b5ae12 100644 --- a/drivers/gpu/drm/imx/ipuv3-plane.c +++ b/drivers/gpu/drm/imx/ipuv3-plane.c @@ -496,6 +496,27 @@ static int ipu_chan_assign_axi_id(int ipu_chan) } }
+static void ipu_calculate_bursts(u32 width, u32 cpp, u32 stride, + u8 *burstsize, u8 *num_bursts) +{ + const unsigned int width_bytes = width * cpp; + unsigned int npb, bursts; + + /* Maximum number of pixels per burst without overshooting stride */ + for (npb = 64 / cpp; npb > 0; --npb) { + if (round_up(width_bytes, npb * cpp) <= stride) + break; + } + *burstsize = npb; + + /* Maximum number of consecutive bursts without overshooting stride */ + for (bursts = 8; bursts > 1; bursts /= 2) { + if (round_up(width_bytes, npb * cpp * bursts) <= stride) + break; + } + *num_bursts = bursts; +} + static void ipu_plane_atomic_update(struct drm_plane *plane, struct drm_plane_state *old_state) { @@ -509,6 +530,9 @@ static void ipu_plane_atomic_update(struct drm_plane *plane, unsigned long alpha_eba = 0; enum ipu_color_space ics; unsigned int axi_id = 0; + const struct drm_format_info *info; + u8 burstsize, num_bursts; + u32 width, height; int active;
if (ipu_plane->dp_flow == IPU_DP_FLOW_SYNC_FG) @@ -583,15 +607,21 @@ static void ipu_plane_atomic_update(struct drm_plane *plane,
ipu_dmfc_config_wait4eot(ipu_plane->dmfc, drm_rect_width(dst));
+ width = drm_rect_width(&state->src) >> 16; + height = drm_rect_height(&state->src) >> 16; + info = drm_format_info(fb->format->format); + ipu_calculate_bursts(width, info->cpp[0], fb->pitches[0], + &burstsize, &num_bursts); + ipu_cpmem_zero(ipu_plane->ipu_ch); - ipu_cpmem_set_resolution(ipu_plane->ipu_ch, - drm_rect_width(&state->src) >> 16, - drm_rect_height(&state->src) >> 16); + ipu_cpmem_set_resolution(ipu_plane->ipu_ch, width, height); ipu_cpmem_set_fmt(ipu_plane->ipu_ch, fb->format->format); + ipu_cpmem_set_burstsize(ipu_plane->ipu_ch, burstsize); ipu_cpmem_set_high_priority(ipu_plane->ipu_ch); ipu_idmac_set_double_buffer(ipu_plane->ipu_ch, 1); ipu_cpmem_set_stride(ipu_plane->ipu_ch, fb->pitches[0]); ipu_cpmem_set_axi_id(ipu_plane->ipu_ch, axi_id); + switch (fb->format->format) { case DRM_FORMAT_YUV420: case DRM_FORMAT_YVU420: @@ -631,6 +661,7 @@ static void ipu_plane_atomic_update(struct drm_plane *plane, case DRM_FORMAT_RGBX8888_A8: case DRM_FORMAT_BGRX8888_A8: alpha_eba = drm_plane_state_to_eba(state, 1); + num_bursts = 0;
dev_dbg(ipu_plane->base.dev->dev, "phys = %lu %lu, x = %d, y = %d", eba, alpha_eba, state->src.x1 >> 16, state->src.y1 >> 16); @@ -656,6 +687,7 @@ static void ipu_plane_atomic_update(struct drm_plane *plane, } ipu_cpmem_set_buffer(ipu_plane->ipu_ch, 0, eba); ipu_cpmem_set_buffer(ipu_plane->ipu_ch, 1, eba); + ipu_idmac_lock_enable(ipu_plane->ipu_ch, num_bursts); ipu_plane_enable(ipu_plane); }