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Message-ID: <rthpkuipbpbp2lv2ddmruwb7fmpkmtlsnx3q6kk7gaskzpdaar@5bk3r44f2mpo>
Date: Mon, 15 Sep 2025 18:55:44 +0200
From: Jacopo Mondi <jacopo.mondi@...asonboard.com>
To: Stefan Klug <stefan.klug@...asonboard.com>
Cc: linux-media@...r.kernel.org,
Jacopo Mondi <jacopo.mondi@...asonboard.com>, Dafna Hirschfeld <dafna@...tmail.com>,
Laurent Pinchart <laurent.pinchart@...asonboard.com>, Mauro Carvalho Chehab <mchehab@...nel.org>,
Heiko Stuebner <heiko@...ech.de>, linux-rockchip@...ts.infradead.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: rkisp1: Improve frame sequence correctness on
stats and params buffers
Hi Stefan
On Mon, Sep 08, 2025 at 11:41:48AM +0200, Stefan Klug wrote:
> On the rkisp1 (in my case on a NXP i.MX8 M Plus) the ISP interrupt
> handler is sometimes called with RKISP1_CIF_ISP_V_START (start of frame)
> and RKISP1_CIF_ISP_FRAME (end of frame) being set at the same time. In
> commit 8524fa22fd2f ("media: staging: rkisp1: isp: add a warning and
> debugfs var for irq delay") a warning was added for that. There are two
> cases where this condition can occur:
>
> 1. The v-sync and the frame-end belong to the same frame. This means,
> the irq was heavily delayed and the warning is likely appropriate.
>
> 2. The v-sync belongs to the next frame. This can happen if the vertical
> blanking between two frames is very short.
>
> The current code always handles case 1 although case 2 is in my
> experience the more common case and happens in regular usage. This leads
I would rather argue that 8524fa22fd2f is possibily wrong, and case 1)
would imply the interrupt has been delayed for the whole frame
duration (+ blanking), which seems unlikely to me ?
True we handle stats collection and parameters programming in irq
context, which is less than ideal and could take time (I wonder if we
should use a threaded irq, but that's a different problem)
If that's the case and we only should care about 2) would simply
handling RKISP1_CIF_ISP_FRAME before RKISP1_CIF_ISP_V_START be enough ?
> to incorrect sequence numbers on stats and params buffers which in turn
> breaks the regulation in user space. Fix that by adding a frame_active
> flag to distinguish between these cases and handle the start of frame
> either at the beginning or at the end of the rkisp1_isp_isr().
>
> Signed-off-by: Stefan Klug <stefan.klug@...asonboard.com>
> ---
> .../platform/rockchip/rkisp1/rkisp1-common.h | 1 +
> .../media/platform/rockchip/rkisp1/rkisp1-isp.c | 17 +++++++++++++----
> 2 files changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/platform/rockchip/rkisp1/rkisp1-common.h b/drivers/media/platform/rockchip/rkisp1/rkisp1-common.h
> index ca952fd0829b..adf23416de9a 100644
> --- a/drivers/media/platform/rockchip/rkisp1/rkisp1-common.h
> +++ b/drivers/media/platform/rockchip/rkisp1/rkisp1-common.h
> @@ -222,6 +222,7 @@ struct rkisp1_isp {
> struct media_pad pads[RKISP1_ISP_PAD_MAX];
> const struct rkisp1_mbus_info *sink_fmt;
> __u32 frame_sequence;
> + bool frame_active;
> };
>
> /*
> diff --git a/drivers/media/platform/rockchip/rkisp1/rkisp1-isp.c b/drivers/media/platform/rockchip/rkisp1/rkisp1-isp.c
> index 8c29a1c9309a..1469075b2d45 100644
> --- a/drivers/media/platform/rockchip/rkisp1/rkisp1-isp.c
> +++ b/drivers/media/platform/rockchip/rkisp1/rkisp1-isp.c
> @@ -965,6 +965,7 @@ static int rkisp1_isp_s_stream(struct v4l2_subdev *sd, int enable)
> }
>
> isp->frame_sequence = -1;
> + isp->frame_active = false;
>
> sd_state = v4l2_subdev_lock_and_get_active_state(sd);
>
> @@ -1086,12 +1087,15 @@ void rkisp1_isp_unregister(struct rkisp1_device *rkisp1)
> * Interrupt handlers
> */
>
> -static void rkisp1_isp_queue_event_sof(struct rkisp1_isp *isp)
> +static void rkisp1_isp_sof(struct rkisp1_isp *isp)
> {
> struct v4l2_event event = {
> .type = V4L2_EVENT_FRAME_SYNC,
> };
>
> + isp->frame_sequence++;
> + isp->frame_active = true;
> +
> event.u.frame_sync.frame_sequence = isp->frame_sequence;
> v4l2_event_queue(isp->sd.devnode, &event);
> }
> @@ -1112,14 +1116,15 @@ irqreturn_t rkisp1_isp_isr(int irq, void *ctx)
> rkisp1_write(rkisp1, RKISP1_CIF_ISP_ICR, status);
>
> /* Vertical sync signal, starting generating new frame */
> - if (status & RKISP1_CIF_ISP_V_START) {
> - rkisp1->isp.frame_sequence++;
> - rkisp1_isp_queue_event_sof(&rkisp1->isp);
> + if (status & RKISP1_CIF_ISP_V_START && !rkisp1->isp.frame_active) {
> + status &= ~RKISP1_CIF_ISP_V_START;
> + rkisp1_isp_sof(&rkisp1->isp);
> if (status & RKISP1_CIF_ISP_FRAME) {
> WARN_ONCE(1, "irq delay is too long, buffers might not be in sync\n");
> rkisp1->debug.irq_delay++;
> }
> }
> +
> if (status & RKISP1_CIF_ISP_PIC_SIZE_ERROR) {
> /* Clear pic_size_error */
> isp_err = rkisp1_read(rkisp1, RKISP1_CIF_ISP_ERR);
> @@ -1138,6 +1143,7 @@ irqreturn_t rkisp1_isp_isr(int irq, void *ctx)
> if (status & RKISP1_CIF_ISP_FRAME) {
> u32 isp_ris;
>
> + rkisp1->isp.frame_active = false;
> rkisp1->debug.complete_frames++;
>
> /* New frame from the sensor received */
> @@ -1152,5 +1158,8 @@ irqreturn_t rkisp1_isp_isr(int irq, void *ctx)
> rkisp1_params_isr(rkisp1);
> }
>
> + if (status & RKISP1_CIF_ISP_V_START && !rkisp1->isp.frame_active)
I think you can drop the && !rkisp1->isp.frame_active because if you
get here and 'status & RKISP1_CIF_ISP_V_START' it means that:
1) frame_active was false and you have entered the above
if (status & RKISP1_CIF_ISP_V_START && !rkisp1->isp.frame_active) {
and now the RKISP1_CIF_ISP_V_START bit in 'status' has been cleared
so you don't need to handle VSYNC here
2) frame_active was true and you delayed handling V_START till here.
If also ISP_FRAME was set, frame_start has been set to false here
above. If ISP_FRAME was not set then it has been delivered by a
previous interrupt and then frame_start is false.
So I guess it's enough to check if at this point RKISP1_CIF_ISP_V_START
is still set in 'status' ?
However, as said, it's seems unlikely to that your above 1) can
happen. Have you ever hit a WARN() again with this patch applied ?
> + rkisp1_isp_sof(&rkisp1->isp);
> +
> return IRQ_HANDLED;
> }
> --
> 2.48.1
>
>
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