linux-kernel - Re: 回复: 回复: 回复: [PATCH] staging: media: starfive: Add multiple resolution support

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Message-ID: <20240819001327.GK29465@pendragon.ideasonboard.com>
Date: Mon, 19 Aug 2024 03:13:27 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Changhuang Liang <changhuang.liang@...rfivetech.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hans Verkuil <hverkuil-cisco@...all.nl>,
	Jack Zhu <jack.zhu@...rfivetech.com>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-staging@...ts.linux.dev" <linux-staging@...ts.linux.dev>
Subject: Re: 回复: 回复: 回复: [PATCH] staging: media: starfive: Add
 multiple resolution support

On Mon, Aug 12, 2024 at 12:13:03PM +0000, Changhuang Liang wrote:
> > On Mon, Aug 12, 2024 at 09:43:47AM +0000, Changhuang Liang wrote:
> > > > On Fri, Aug 09, 2024 at 12:12:01PM +0000, Changhuang Liang wrote:
> > > > > > On Fri, Apr 19, 2024 at 01:19:55AM -0700, Changhuang Liang wrote:
> > > > > > > Add multiple resolution support for video "capture_raw" device.
> > > > > > > Otherwise it will capture the wrong image data if the width is not 1920.
> > > > > > >
> > > > > > > Fixes: e080f339c80a ("media: staging: media: starfive: camss:
> > > > > > > Add capture driver")
> > > > > > >
> > > > > > > Signed-off-by: Changhuang Liang
> > > > > > > <changhuang.liang@...rfivetech.com>
> > > > > > > ---
> > > > > > >  drivers/staging/media/starfive/camss/stf-capture.c | 5 ++++-
> > > > > > >  1 file changed, 4 insertions(+), 1 deletion(-)
> > > > > > >
> > > > > > > diff --git
> > > > > > > a/drivers/staging/media/starfive/camss/stf-capture.c
> > > > > > > b/drivers/staging/media/starfive/camss/stf-capture.c
> > > > > > > index ec5169e7b391..9e853ff2596a 100644
> > > > > > > --- a/drivers/staging/media/starfive/camss/stf-capture.c
> > > > > > > +++ b/drivers/staging/media/starfive/camss/stf-capture.c
> > > > > > > @@ -177,9 +177,12 @@ static void stf_channel_set(struct
> > > > > > > stfcamss_video
> > > > > > > *video)  {
> > > > > > >  	struct stf_capture *cap = to_stf_capture(video);
> > > > > > >  	struct stfcamss *stfcamss = cap->video.stfcamss;
> > > > > > > +	struct v4l2_pix_format *pix;
> > > > > >
> > > > > > This variable can be const as you don't modify the format.
> > > > > >
> > > > > > >  	u32 val;
> > > > > > >
> > > > > > >  	if (cap->type == STF_CAPTURE_RAW) {
> > > > > > > +		pix = &video->active_fmt.fmt.pix;
> > > > > >
> > > > > > And it can be declared and initialized here:
> > > > > >
> > > > > > 		const struct v4l2_pix_format *pix =
> > > > > > &video->active_fmt.fmt.pix;
> > > > > >
> > > > > > > +
> > > > > > >  		val = stf_syscon_reg_read(stfcamss, VIN_CHANNEL_SEL_EN);
> > > > > > >  		val &= ~U0_VIN_CHANNEL_SEL_MASK;
> > > > > > >  		val |= CHANNEL(0);
> > > > > > > @@ -193,7 +196,7 @@ static void stf_channel_set(struct stfcamss_video *video)
> > > > > > >  		val |= PIXEL_HEIGH_BIT_SEL(0);
> > > > > > >
> > > > > > >  		val &= ~U0_VIN_PIX_CNT_END_MASK;
> > > > > > > -		val |= PIX_CNT_END(IMAGE_MAX_WIDTH / 4 - 1);
> > > > > > > +		val |= PIX_CNT_END(pix->width / 4 - 1);
> > > > > >
> > > > > > Is there no need to consider the image height as well ? How does
> > > > > > the driver prevent buffer overflows if the sensor sends more data than expected ?
> > > > >
> > > > > Our hardware will confirm a frame of data through vblank signal,
> > > > > so there is no image height configuration.
> > > >
> > > > What happens if the system expects, for instance, a 1920x1080 RAW8
> > > > image, and allocates a buffer of of 1920x1080 bytes, but the sensor
> > > > outputs more lines ? Does the camera hardware in the SoC offer an
> > > > option to prevent buffer overruns ?
> > >
> > > The hardware can confirm the image height by using the VSYNC signal.
> > >
> > > Image will transfer when VSYNC is high.
> > >
> > > VSYNC time = (width + h_blank) * height;
> > 
> > What I'm trying to understand is what happens if the ISP is configured for
> > 1080 lines, but the camera sensor sends more than 1080 lines (the VSYNC
> > signal is active for more than 1080 lines). Where in the driver is the hardware
> > configure with the 1080 lines limit to avoid buffer overflows ?
> 
> If is "capture_raw" video device, no image height can be configured.

In that case what happens if the camera sensor sends more lines than
expected ? Will the raw video device write past the end of the buffer ?
If so, is there a way to guard against that ?

> If is "capture_yuv" video device, it will be set by stf_isp_config_crop.

Thank you, that's the information I was looking for.

-- 
Regards,

Laurent Pinchart