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Message-ID: <CAEHHSvaePj2MUg+zgmkpZF4HTj_F9ED0RxuzQr2oOAUJgOieng@mail.gmail.com>
Date: Fri, 22 Nov 2024 10:25:39 +0100
From: Julien Stephan <jstephan@...libre.com>
To: CK Hu (胡俊光) <ck.hu@...iatek.com>
Cc: "mchehab@...nel.org" <mchehab@...nel.org>, "conor+dt@...nel.org" <conor+dt@...nel.org>,
"robh@...nel.org" <robh@...nel.org>, Andy Hsieh (謝智皓) <Andy.Hsieh@...iatek.com>,
"matthias.bgg@...il.com" <matthias.bgg@...il.com>,
"laurent.pinchart@...asonboard.com" <laurent.pinchart@...asonboard.com>,
"krzk+dt@...nel.org" <krzk+dt@...nel.org>,
AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"paul.elder@...asonboard.com" <paul.elder@...asonboard.com>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
"fsylvestre@...libre.com" <fsylvestre@...libre.com>, "pnguyen@...libre.com" <pnguyen@...libre.com>
Subject: Re: [PATCH v7 4/5] media: platform: mediatek: isp: add mediatek
ISP3.0 camsv
Le ven. 22 nov. 2024 à 09:41, CK Hu (胡俊光) <ck.hu@...iatek.com> a écrit :
>
> Hi, Julien:
>
> On Thu, 2024-11-21 at 09:53 +0100, Julien Stephan wrote:
> > External email : Please do not click links or open attachments until you have verified the sender or the content.
> >
> >
> > From: Phi-bang Nguyen <pnguyen@...libre.com>
> >
> > This driver provides a path to bypass the SoC ISP so that image data
> > coming from the SENINF can go directly into memory without any image
> > processing. This allows the use of an external ISP.
> >
> > Signed-off-by: Phi-bang Nguyen <pnguyen@...libre.com>
> > Signed-off-by: Florian Sylvestre <fsylvestre@...libre.com>
> > [Paul Elder fix irq locking]
> > Signed-off-by: Paul Elder <paul.elder@...asonboard.com>
> > Co-developed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > Signed-off-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> > Co-developed-by: Julien Stephan <jstephan@...libre.com>
> > Signed-off-by: Julien Stephan <jstephan@...libre.com>
> > ---
>
> [snip]
>
> > +static irqreturn_t isp_irq_camsv30(int irq, void *data)
> > +{
> > + struct mtk_cam_dev *cam_dev = (struct mtk_cam_dev *)data;
> > + struct mtk_cam_dev_buffer *buf;
> > + unsigned int irq_status;
> > +
> > + spin_lock(&cam_dev->buf_list_lock);
> > +
> > + irq_status = mtk_camsv30_read(cam_dev, CAMSV_INT_STATUS);
> > +
> > + if (irq_status & INT_ST_MASK_CAMSV_ERR)
> > + dev_err(cam_dev->dev, "irq error 0x%lx\n",
> > + irq_status & INT_ST_MASK_CAMSV_ERR);
> > +
> > + /* De-queue frame */
> > + if (irq_status & CAMSV_IRQ_PASS1_DON) {
> > + cam_dev->sequence++;
> > +
> > + buf = list_first_entry_or_null(&cam_dev->buf_list,
> > + struct mtk_cam_dev_buffer,
> > + list);
> > + if (buf) {
> > + buf->v4l2_buf.sequence = cam_dev->sequence;
> > + buf->v4l2_buf.vb2_buf.timestamp =
> > + ktime_get_ns();
> > + vb2_buffer_done(&buf->v4l2_buf.vb2_buf,
> > + VB2_BUF_STATE_DONE);
> > + list_del(&buf->list);
> > + }
> > +
> > + buf = list_first_entry_or_null(&cam_dev->buf_list,
> > + struct mtk_cam_dev_buffer,
> > + list);
> > + if (buf)
> > + mtk_camsv30_update_buffers_add(cam_dev, buf);
>
> If buf == NULL, so hardware would automatically stop DMA?
> I don't know how this hardware work.
> Below is my imagine about this hardware.
>
> 1. Software use CAMSV_IMGO_FBC_RCNT_INC to increase software buffer index.
> 2. Hardware has a hardware buffer index. After hardware finish one frame, hardware buffer index increase.
> 3. After software buffer index increase, hardware start DMA.
> 4. When hardware buffer index is equal to software buffer index, hardware automatically stop DMA.
>
> Does the hardware work as my imagine?
> If hardware could automatically stop DMA, add comment to describe.
> If hardware could not automatically stop DMA, software should do something to stop DMA when buf == NULL.
>
You are right except that dma is not stopped but frames are
automatically dropped by hardware until a new buffer is enqueued and
software uses CAMSV_IMGO_FBC_RCNT_INC to increase the software buffer
index.
What about adding the following comment:
/*
* If there is no user buffer available, hardware will drop automatically
* frames until buf_queue is called
*/
Let me know if that works for you
Cheers
Julien
> Regards,
> CK
>
> > + }
> > +
> > + spin_unlock(&cam_dev->buf_list_lock);
> > +
> > + return IRQ_HANDLED;
> > +}
> > +
>
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