[PATCH 6.0 0261/1073] drm: lcdif: change burst size to 256B

Greg Kroah-Hartman
2022-12-28T15:27:57Z

From: Marco Felsch <m.felsch@pengutronix.de>

[ Upstream commit 2215cb3be5c28a1fd43036550c00c2371aeeba95 ]

If a axi bus master with a higher priority do a lot of memory access
FIFO underruns can be inspected. Increase the burst size to 256B to
avoid such underruns and to improve the memory access efficiency.

Fixes: 9db35bb349a0 ("drm: lcdif: Add support for i.MX8MP LCDIF variant")
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20221101164615.778299-1-m.felsch@pengutronix.de
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/gpu/drm/mxsfb/lcdif_kms.c | 14 ++++++++++++--
drivers/gpu/drm/mxsfb/lcdif_regs.h | 4 ++++
2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/mxsfb/lcdif_kms.c b/drivers/gpu/drm/mxsfb/lcdif_kms.c
index 11f881554f74..713b0d756f2a 100644
--- a/drivers/gpu/drm/mxsfb/lcdif_kms.c
+++ b/drivers/gpu/drm/mxsfb/lcdif_kms.c
@@ -149,8 +149,18 @@ static void lcdif_set_mode(struct lcdif_drm_private *lcdif, u32 bus_flags)
CTRLDESCL0_1_WIDTH(m->crtc_hdisplay),
lcdif->base + LCDC_V8_CTRLDESCL0_1);

- writel(CTRLDESCL0_3_PITCH(lcdif->crtc.primary->state->fb->pitches[0]),
- lcdif->base + LCDC_V8_CTRLDESCL0_3);
+ /*
+ * Undocumented P_SIZE and T_SIZE register but those written in the
+ * downstream kernel those registers control the AXI burst size. As of
+ * now there are two known values:
+ * 1 - 128Byte
+ * 2 - 256Byte
+ * Downstream set it to 256B burst size to improve the memory
+ * efficiency so set it here too.
+ */
+ ctrl = CTRLDESCL0_3_P_SIZE(2) | CTRLDESCL0_3_T_SIZE(2) |
+ CTRLDESCL0_3_PITCH(lcdif->crtc.primary->state->fb->pitches[0]);
+ writel(ctrl, lcdif->base + LCDC_V8_CTRLDESCL0_3);
}

static void lcdif_enable_controller(struct lcdif_drm_private *lcdif)
diff --git a/drivers/gpu/drm/mxsfb/lcdif_regs.h b/drivers/gpu/drm/mxsfb/lcdif_regs.h
index c70220651e3a..8e8bef175bf2 100644
--- a/drivers/gpu/drm/mxsfb/lcdif_regs.h
+++ b/drivers/gpu/drm/mxsfb/lcdif_regs.h
@@ -190,6 +190,10 @@
#define CTRLDESCL0_1_WIDTH(n) ((n) & 0xffff)
#define CTRLDESCL0_1_WIDTH_MASK GENMASK(15, 0)

+#define CTRLDESCL0_3_P_SIZE(n) (((n) << 20) & CTRLDESCL0_3_P_SIZE_MASK)
+#define CTRLDESCL0_3_P_SIZE_MASK GENMASK(22, 20)
+#define CTRLDESCL0_3_T_SIZE(n) (((n) << 16) & CTRLDESCL0_3_T_SIZE_MASK)
+#define CTRLDESCL0_3_T_SIZE_MASK GENMASK(17, 16)
#define CTRLDESCL0_3_PITCH(n) ((n) & 0xffff)
#define CTRLDESCL0_3_PITCH_MASK GENMASK(15, 0)

--
2.35.1