linux-kernel - Re: [PATCH v1 5/5] drivers: media: bcm2835-unicam: Correctly handle FS + FE ISR condition

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Message-ID: <xy44zndazbw7ehpzbc6hexgptjymevvupjhuy2x6zxp54qtepm@vlbb6js62cq4>
Date: Fri, 22 Nov 2024 12:16:32 +0100
From: Jacopo Mondi <jacopo.mondi@...asonboard.com>
To: Naushir Patuck <naush@...pberrypi.com>
Cc: Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>, 
	Mauro Carvalho Chehab <mchehab@...nel.org>, Florian Fainelli <florian.fainelli@...adcom.com>, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, Ray Jui <rjui@...adcom.com>, 
	Scott Branden <sbranden@...adcom.com>, linux-media@...r.kernel.org, 
	linux-rpi-kernel@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, jacopo.mondi@...asonboard.com, 
	Dave Stevenson <dave.stevenson@...pberrypi.com>
Subject: Re: [PATCH v1 5/5] drivers: media: bcm2835-unicam: Correctly handle
 FS + FE ISR condition

Hi Naush

On Fri, Nov 22, 2024 at 08:41:52AM +0000, Naushir Patuck wrote:
> This change aligns the FS/FE interrupt handling with the Raspberry Pi
> kernel downstream Unicam driver.
>
> If we get a simultaneous FS + FE interrupt for the same frame, it cannot
> be marked as completed and returned to userland as the framebuffer will
> be refilled by Unicam on the next sensor frame. Additionally, the
> timestamp will be set to 0 as the FS interrupt handling code will not
> have run yet.
>
> To avoid these problems, the frame is considered dropped in the FE
> handler, and will be returned to userland on the subsequent sensor frame.
>
> Signed-off-by: Naushir Patuck <naush@...pberrypi.com>
> ---
>  .../media/platform/broadcom/bcm2835-unicam.c  | 39 +++++++++++++++++--
>  1 file changed, 35 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/platform/broadcom/bcm2835-unicam.c b/drivers/media/platform/broadcom/bcm2835-unicam.c
> index f10064107d54..0d2aa25d483f 100644
> --- a/drivers/media/platform/broadcom/bcm2835-unicam.c
> +++ b/drivers/media/platform/broadcom/bcm2835-unicam.c
> @@ -773,10 +773,26 @@ static irqreturn_t unicam_isr(int irq, void *dev)
>  			 * as complete, as the HW will reuse that buffer.
>  			 */
>  			if (node->cur_frm && node->cur_frm != node->next_frm) {
> +				/*
> +				 * This condition checks if FE + FS for the same
> +				 * frame has occurred. In such cases, we cannot
> +				 * return out the frame, as no buffer handling
> +				 * or timestamping has yet been done as part of
> +				 * the FS handler.
> +				 */
> +				if (!node->cur_frm->vb.vb2_buf.timestamp) {
> +					dev_dbg(unicam->v4l2_dev.dev,
> +						"ISR: FE without FS, dropping frame\n");
> +					continue;
> +				}
> +
>  				unicam_process_buffer_complete(node, sequence);
> +				node->cur_frm = node->next_frm;
> +				node->next_frm = NULL;
>  				inc_seq = true;
> +			} else {
> +				node->cur_frm = node->next_frm;
>  			}
> -			node->cur_frm = node->next_frm;
>  		}
>
>  		/*
> @@ -812,10 +828,25 @@ static irqreturn_t unicam_isr(int irq, void *dev)
>  					i);
>  			/*
>  			 * Set the next frame output to go to a dummy frame
> -			 * if we have not managed to obtain another frame
> -			 * from the queue.
> +			 * if no buffer currently queued.
>  			 */
> -			unicam_schedule_dummy_buffer(node);
> +			if (!node->next_frm ||
> +			    node->next_frm == node->cur_frm) {
> +				unicam_schedule_dummy_buffer(node);
> +			} else if (unicam->node[i].cur_frm) {
> +				/*
> +				 * Repeated FS without FE. Hardware will have
> +				 * swapped buffers, but the cur_frm doesn't
> +				 * contain valid data. Return cur_frm to the
> +				 * queue.

So the buffer gets silently recycled ? Or should it be returned with
errors to userspace ?

> +				 */
> +				spin_lock(&node->dma_queue_lock);
> +				list_add_tail(&node->cur_frm->list,
> +					      &node->dma_queue);
> +				spin_unlock(&node->dma_queue_lock);
> +				node->cur_frm = node->next_frm;
> +				node->next_frm = NULL;
> +			}
>  		}
>
>  		unicam_queue_event_sof(unicam);
> --
> 2.34.1
>
>