[PATCH] media: rkvdec: vdpu383: configure the reference read cache
From: Valerii Bokov via B4 Relay
Date: Wed Oct 28 2026 - 07:27:30 EST
From: Valerii Bokov <vlry.bkv@xxxxxxxxx>
The VDPU383 has a reference read cache with its own register region,
"cache" in the device tree, which the driver does not map. Its
configuration and read limit are therefore left at their power-on
values, and those differ between power-ups. On RK3576 this makes H.264
decoding of a 2688x1520 stream take either 22.5 ms or 65.4 ms per
frame, depending on the power-up, while the values the vendor driver
programs bring it to 3.6 ms per frame.
Map the "cache" region and, as the vendor driver does before every
frame, enable cacheable read-allocate accesses with 64-byte lines,
clear the cache and set the read limit (MAX_READS in the vendor
driver) to 0x1c. The cache is cleared on every run because reference
buffers are rewritten between frames.
Decode time per frame for a 2688x1520 H.264 stream on RK3576, within
one decoder power-up, with the registers set between runs:
MAX_READS CACHE0_CFG ms/frame
0x0 power-on 65.4 (slow power-up)
0x2 power-on 22.5 (fast power-up)
0x1c power-on 7.2
0x2 0x13 8.6
0x1c 0x13 3.6
The decoded output was bit-identical in all five cases. These numbers
were taken by setting the registers from user space through /dev/mem.
With this patch applied, a 2688x1520 recording from the same camera
decodes at 3.55-3.60 ms per frame on every decoder power-up (8 of 8
runs), and the decoded output is bit-identical to FFmpeg's software
decoder (751 frames).
The registers were identified with the help of an AI coding assistant
(Claude), by diffing register dumps of fast and slow power-ups and
comparing them with the vendor driver (rkvdec_vdpu38x_run() in
mpp_rkvdec2.c); the assistant also drafted this patch.
Link: https://lists.infradead.org/pipermail/linux-rockchip/2026-June/072308.html
Signed-off-by: Valerii Bokov <vlry.bkv@xxxxxxxxx>
---
.../platform/rockchip/rkvdec/rkvdec-vdpu383-h264.c | 2 ++
.../platform/rockchip/rkvdec/rkvdec-vdpu383-hevc.c | 2 ++
.../platform/rockchip/rkvdec/rkvdec-vdpu383-regs.h | 8 ++++++++
drivers/media/platform/rockchip/rkvdec/rkvdec.c | 19 +++++++++++++++++++
drivers/media/platform/rockchip/rkvdec/rkvdec.h | 2 ++
5 files changed, 33 insertions(+)
diff --git a/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-h264.c b/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-h264.c
index 5ec755733..572ff404d 100644
--- a/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-h264.c
+++ b/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-h264.c
@@ -441,6 +441,8 @@ static int rkvdec_h264_run(struct rkvdec_ctx *ctx)
timeout_threshold = h264_ctx->regs.common.reg013_core_timeout_threshold;
rkvdec_schedule_watchdog(rkvdec, timeout_threshold);
+ rkvdec_vdpu383_setup_cache(rkvdec);
+
/* Start decoding! */
writel(timeout_threshold, rkvdec->link + VDPU383_LINK_TIMEOUT_THRESHOLD);
writel(0, rkvdec->link + VDPU383_LINK_IP_ENABLE);
diff --git a/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-hevc.c b/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-hevc.c
index 3462d995d..f2f811b0f 100644
--- a/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-hevc.c
+++ b/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-hevc.c
@@ -568,6 +568,8 @@ static int rkvdec_hevc_run(struct rkvdec_ctx *ctx)
timeout_threshold = hevc_ctx->regs.common.reg013_core_timeout_threshold;
rkvdec_schedule_watchdog(rkvdec, timeout_threshold);
+ rkvdec_vdpu383_setup_cache(rkvdec);
+
/* Start decoding! */
writel(timeout_threshold, rkvdec->link + VDPU383_LINK_TIMEOUT_THRESHOLD);
writel(VDPU383_IP_CRU_MODE, rkvdec->link + VDPU383_LINK_IP_ENABLE);
diff --git a/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-regs.h b/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-regs.h
index 04eb23297..e04b5ce1c 100644
--- a/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-regs.h
+++ b/drivers/media/platform/rockchip/rkvdec/rkvdec-vdpu383-regs.h
@@ -42,6 +42,14 @@
#define VDPU383_STA_INT_SOFTRESET_RDY (BIT(10) | BIT(11))
#define VDPU383_STA_INT_ALL 0x3ff
+/* Reference read cache, in the "cache" register region */
+#define VDPU383_CACHE_CLR_CACHE0 0x10
+#define VDPU383_CACHE_MAX_READS 0x18
+#define VDPU383_CACHE_CACHE0_CFG 0x1c
+#define VDPU383_CACHE_CFG_CACHEABLE BIT(0)
+#define VDPU383_CACHE_CFG_READ_ALLOCATE BIT(1)
+#define VDPU383_CACHE_CFG_LINE_64B BIT(4)
+
struct vdpu383_regs_common {
u32 reg008_dec_mode;
diff --git a/drivers/media/platform/rockchip/rkvdec/rkvdec.c b/drivers/media/platform/rockchip/rkvdec/rkvdec.c
index fbcd0f175..c609e8c69 100644
--- a/drivers/media/platform/rockchip/rkvdec/rkvdec.c
+++ b/drivers/media/platform/rockchip/rkvdec/rkvdec.c
@@ -1158,6 +1158,21 @@ void rkvdec_schedule_watchdog(struct rkvdec_dev *rkvdec, u32 timeout_threshold)
schedule_delayed_work(&rkvdec->watchdog_work, msecs_to_jiffies(watchdog_time));
}
+/*
+ * The reference read cache and the read limit are left at their power-on
+ * values otherwise, which vary between power-ups and make decoding several
+ * times slower. Program them as the vendor driver does, before every frame:
+ * the cache is cleared each time because reference buffers are rewritten
+ * between frames.
+ */
+void rkvdec_vdpu383_setup_cache(struct rkvdec_dev *rkvdec)
+{
+ writel(VDPU383_CACHE_CFG_CACHEABLE | VDPU383_CACHE_CFG_READ_ALLOCATE |
+ VDPU383_CACHE_CFG_LINE_64B, rkvdec->cache + VDPU383_CACHE_CACHE0_CFG);
+ writel(1, rkvdec->cache + VDPU383_CACHE_CLR_CACHE0);
+ writel(0x1c, rkvdec->cache + VDPU383_CACHE_MAX_READS);
+}
+
static void rkvdec_device_run(void *priv)
{
struct rkvdec_ctx *ctx = priv;
@@ -1807,6 +1822,10 @@ static int rkvdec_probe(struct platform_device *pdev)
rkvdec->link = devm_platform_ioremap_resource_byname(pdev, "link");
if (IS_ERR(rkvdec->link))
return PTR_ERR(rkvdec->link);
+
+ rkvdec->cache = devm_platform_ioremap_resource_byname(pdev, "cache");
+ if (IS_ERR(rkvdec->cache))
+ return PTR_ERR(rkvdec->cache);
}
ret = dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32));
diff --git a/drivers/media/platform/rockchip/rkvdec/rkvdec.h b/drivers/media/platform/rockchip/rkvdec/rkvdec.h
index a24be6638..f97eaef3a 100644
--- a/drivers/media/platform/rockchip/rkvdec/rkvdec.h
+++ b/drivers/media/platform/rockchip/rkvdec/rkvdec.h
@@ -136,6 +136,7 @@ struct rkvdec_dev {
struct clk *axi_clk;
void __iomem *regs;
void __iomem *link;
+ void __iomem *cache;
struct mutex vdev_lock; /* serializes ioctls */
struct delayed_work watchdog_work;
struct gen_pool *sram_pool;
@@ -180,6 +181,7 @@ void rkvdec_run_preamble(struct rkvdec_ctx *ctx, struct rkvdec_run *run);
void rkvdec_run_postamble(struct rkvdec_ctx *ctx, struct rkvdec_run *run);
void rkvdec_memcpy_toio(void __iomem *dst, void *src, size_t len);
void rkvdec_schedule_watchdog(struct rkvdec_dev *rkvdec, u32 timeout_threshold);
+void rkvdec_vdpu383_setup_cache(struct rkvdec_dev *rkvdec);
void rkvdec_quirks_disable_qos(struct rkvdec_ctx *ctx);
---
base-commit: 65ba8f34ec886ec72b2c07ddc8cf3d815c32869d
change-id: 20261028-rkvdec-vdpu383-cache-8fbbf8313da3
Best regards,
--
Valerii Bokov <vlry.bkv@xxxxxxxxx>