Re: [PATCH v8 3/6] staging: media: Add support for the Allwinner A31 ISP

[Conor Dooley <conor@kernel.org>]

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On Sun, Nov 27, 2022 at 11:31:41PM -0700, Nathan Chancellor wrote:
> Hi Paul,
> 
> On Thu, Nov 03, 2022 at 05:37:14PM +0100, Paul Kocialkowski wrote:
> > Some Allwinner platforms come with an Image Signal Processor, which
> > supports various features in order to enhance and transform data
> > received by image sensors into good-looking pictures. In most cases,
> > the data is raw bayer, which gets internally converted to RGB and
> > finally YUV, which is what the hardware produces.
> > 
> > This driver supports ISPs that are similar to the A31 ISP, which was
> > the first standalone ISP found in Allwinner platforms. Simpler ISP
> > blocks were found in the A10 and A20, where they are tied to a CSI
> > controller. Newer generations of Allwinner SoCs (starting with the
> > H6, H616, etc) come with a new camera subsystem and revised ISP.
> > Even though these previous and next-generation ISPs are somewhat
> > similar to the A31 ISP, they have enough significant differences to
> > be out of the scope of this driver.
> > 
> > While the ISP supports many features, including 3A and many
> > enhancement blocks, this implementation is limited to the following:
> > - V3s (V3/S3) platform support;
> > - Bayer media bus formats as input;
> > - Semi-planar YUV (NV12/NV21) as output;
> > - Debayering with per-component gain and offset configuration;
> > - 2D noise filtering with configurable coefficients.
> > 
> > Since many features are missing from the associated uAPI, the driver
> > is aimed to integrate staging until all features are properly
> > described.
> > 
> > On the technical side, it uses the v4l2 and media controller APIs,
> > with a video node for capture, a processor subdev and a video node
> > for parameters submission. A specific uAPI structure and associated
> > v4l2 meta format are used to configure parameters of the supported
> > modules.
> > 
> > One particular thing about the hardware is that configuration for
> > module registers needs to be stored in a DMA buffer and gets copied
> > to actual registers by the hardware at the next vsync, when instructed
> > by a flag. This is handled by the "state" mechanism in the driver.
> > 
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> 
> This patch is now in -next as commit e3185e1d7c14 ("media: staging:
> media: Add support for the Allwinner A31 ISP"), where it causes the
> following clang warnings:

FWIW, this is (as yet) unfixed & thus breaking allmodconfig w/ clang.
I had a quick look on lore but could not see a proposed fix other than
what Nathan has pasted below.

> > +void sun6i_isp_capture_configure(struct sun6i_isp_device *isp_dev)
> > +{
> > +	unsigned int width, height;
> > +	unsigned int stride_luma, stride_chroma = 0;
> > +	unsigned int stride_luma_div4, stride_chroma_div4;
> > +	const struct sun6i_isp_capture_format *format;
> > +	const struct v4l2_format_info *info;
> > +	u32 pixelformat;
> > +
> > +	sun6i_isp_capture_dimensions(isp_dev, &width, &height);
> > +	sun6i_isp_capture_format(isp_dev, &pixelformat);
> > +
> > +	format = sun6i_isp_capture_format_find(pixelformat);
> > +	if (WARN_ON(!format))
> > +		return;
> > +
> > +	sun6i_isp_load_write(isp_dev, SUN6I_ISP_MCH_SIZE_CFG_REG,
> > +			     SUN6I_ISP_MCH_SIZE_CFG_WIDTH(width) |
> > +			     SUN6I_ISP_MCH_SIZE_CFG_HEIGHT(height));
> > +
> > +	info = v4l2_format_info(pixelformat);
> > +	if (WARN_ON(!info))
> > +		return;
> > +
> > +	stride_luma = width * info->bpp[0];
> > +	stride_luma_div4 = DIV_ROUND_UP(stride_luma, 4);
> > +
> > +	if (info->comp_planes > 1) {
> > +		stride_chroma = width * info->bpp[1] / info->hdiv;
> > +		stride_chroma_div4 = DIV_ROUND_UP(stride_chroma, 4);
> > +	}
> > +
> > +	sun6i_isp_load_write(isp_dev, SUN6I_ISP_MCH_CFG_REG,
> > +			     SUN6I_ISP_MCH_CFG_EN |
> > +			     SUN6I_ISP_MCH_CFG_OUTPUT_FMT(format->output_format) |
> > +			     SUN6I_ISP_MCH_CFG_STRIDE_Y_DIV4(stride_luma_div4) |
> > +			     SUN6I_ISP_MCH_CFG_STRIDE_UV_DIV4(stride_chroma_div4));
> > +}
> 
> 
>   drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c:135:6: error: variable 'stride_chroma_div4' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>           if (info->comp_planes > 1) {
>               ^~~~~~~~~~~~~~~~~~~~~
>   drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c:144:42: note: uninitialized use occurs here
>                               SUN6I_ISP_MCH_CFG_STRIDE_UV_DIV4(stride_chroma_div4));
>                                                                 ^~~~~~~~~~~~~~~~~~
>   drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_reg.h:249:48: note: expanded from macro 'SUN6I_ISP_MCH_CFG_STRIDE_UV_DIV4'
>   #define SUN6I_ISP_MCH_CFG_STRIDE_UV_DIV4(v)     (((v) << 20) & GENMASK(30, 20))
>                                                     ^
>   drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c:135:2: note: remove the 'if' if its condition is always true
>           if (info->comp_planes > 1) {
>           ^~~~~~~~~~~~~~~~~~~~~~~~~~~
>   drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c:112:51: note: initialize the variable 'stride_chroma_div4' to silence this warning
>           unsigned int stride_luma_div4, stride_chroma_div4;
>                                                           ^
>                                                             = 0
> 
> Does stride_chroma_div4 want to just be initialized to zero?
> 
> > +static int sun6i_isp_proc_notifier_bound(struct v4l2_async_notifier *notifier,
> > +					 struct v4l2_subdev *remote_subdev,
> > +					 struct v4l2_async_subdev *async_subdev)
> > +{
> > +	struct sun6i_isp_device *isp_dev =
> > +		container_of(notifier, struct sun6i_isp_device, proc.notifier);
> > +	struct sun6i_isp_proc_async_subdev *proc_async_subdev =
> > +		container_of(async_subdev, struct sun6i_isp_proc_async_subdev,
> > +			     async_subdev);
> > +	struct sun6i_isp_proc *proc = &isp_dev->proc;
> > +	struct sun6i_isp_proc_source *source = proc_async_subdev->source;
> > +	bool enabled;
> > +
> > +	switch (source->endpoint.base.port) {
> > +	case SUN6I_ISP_PORT_CSI0:
> > +		source = &proc->source_csi0;
> > +		enabled = true;
> > +		break;
> > +	case SUN6I_ISP_PORT_CSI1:
> > +		source = &proc->source_csi1;
> > +		enabled = !proc->source_csi0.expected;
> > +		break;
> > +	default:
> > +		break;
> > +	}
> > +
> > +	source->subdev = remote_subdev;
> > +
> > +	return sun6i_isp_proc_link(isp_dev, SUN6I_ISP_PROC_PAD_SINK_CSI,
> > +				   remote_subdev, enabled);
> > +}
> 
>   drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_proc.c:418:2: error: variable 'enabled' is used uninitialized whenever switch default is taken [-Werror,-Wsometimes-uninitialized]
>           default:
>           ^~~~~~~
>   drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_proc.c:425:23: note: uninitialized use occurs here
>                                     remote_subdev, enabled);
>                                                     ^~~~~~~
>   drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_proc.c:407:14: note: initialize the variable 'enabled' to silence this warning
>           bool enabled;
>                       ^
>                       = 0
> 
> Should there be an early return in the default case?
> 
> I do not mind sending patches if you are unable to, assuming I have the
> right fixes.
> 
> Cheers,
> Nathan
> 

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