Re: [PATCH v2 3/9] v4l: platform: Add Renesas CEU driver

jacopo mondi
2018-01-03T10:47:57Z

Hi Laurent,

On Tue, Jan 02, 2018 at 03:46:27PM +0200, Laurent Pinchart wrote:
> Hi Jacopo,
>
> Thank you for the patch.
>
> > +/*
> > + * ceu_device - CEU device instance
> > + */
> > +struct ceu_device {
> > + struct device *dev;
> > + struct video_device vdev;
> > + struct v4l2_device v4l2_dev;
> > +
> > + /* subdevices descriptors */
> > + struct ceu_subdev *subdevs;
> > + /* the subdevice currently in use */
> > + struct ceu_subdev *sd;
> > + unsigned int sd_index;
> > + unsigned int num_sd;
> > +
> > + /* platform specific mask with all IRQ sources flagged */
> > + u32 irq_mask;
> > +
> > + /* currently configured field and pixel format */
> > + enum v4l2_field field;
> > + struct v4l2_pix_format_mplane v4l2_pix;
> > +
> > + /* async subdev notification helpers */
> > + struct v4l2_async_notifier notifier;
> > + /* pointers to "struct ceu_subdevice -> asd" */
> > + struct v4l2_async_subdev **asds;
> > +
> > + /* vb2 queue, capture buffer list and active buffer pointer */
> > + struct vb2_queue vb2_vq;
> > + struct list_head capture;
> > + struct vb2_v4l2_buffer *active;
> > + unsigned int sequence;
> > +
> > + /* mlock - lock device suspend/resume and videobuf2 operations */
>
> In my review of v1 I commented that lock documentation should explain what
> data is protected by the lock. As my point seems not to have come across it
> must not have been clear enough, I'll try to fix that.
>
> The purpose of a lock is to protect from concurrent access to a resource. In
> device drivers resources are in most cases either in-memory data or device
> registers. To design a good locking scheme you need to ask yourself what
> resources can be accessed concurrently, and then protect all accesses to those
> resources using locking primitives. Some accesses don't need to be protected
> (for instance it's common to initialize structure fields in the probe function
> where no concurrent access from userspace can occur as device nodes are not
> registered yet), and locking can then be omitted in a case by case basis.
>
> Lock documentation is essential to understand the locking scheme and should
> explain what resources are protected by the lock. It's tempting (because it's
> easy) to instead focus on what code sections the lock covers, but that's not
> how the locking scheme should be designed, and will eventually be prone to
> bugs leading to race conditions.

Thanks, I got this, but that lock is used to protect concurrent
accesses to suspend/resume (and thus interface reset) and is used as
vb2 queue lock. I can mention it guards concurrent interfaces resets,
but I don't see it being that much different from what I already
mentioned.

>
> Obviously a lock will end up preventing multiple code sections from running at
> the same time, but that's the consequence of the locking scheme, it shouldn't
> be its cause.
>
> > + struct mutex mlock;
> > +
> > + /* lock - lock access to capture buffer queue and active buffer */
> > + spinlock_t lock;
> > +
> > + /* base - CEU memory base address */
> > + void __iomem *base;
> > +};
>
> [snip]
>
> > +/*
> > + * ceu_soft_reset() - Software reset the CEU interface
> > + * @ceu_device: CEU device.
> > + *
> > + * Returns 0 for success, -EIO for error.
> > + */
> > +static int ceu_soft_reset(struct ceu_device *ceudev)
> > +{
> > + unsigned int i;
> > +
> > + ceu_write(ceudev, CEU_CAPSR, CEU_CAPSR_CPKIL);
> > +
> > + for (i = 0; i < 100; i++) {
> > + udelay(1);
>
> How about moving the delay after the check in case the condition is true
> immediately ?
>
> > + if (!(ceu_read(ceudev, CEU_CSTSR) & CEU_CSTRST_CPTON))
> > + break;
> > + }
> > +
> > + if (i == 100) {
> > + dev_err(ceudev->dev, "soft reset time out\n");
> > + return -EIO;
> > + }
> > +
> > + for (i = 0; i < 100; i++) {
> > + udelay(1);
>
> Same here.
>
> > + if (!(ceu_read(ceudev, CEU_CAPSR) & CEU_CAPSR_CPKIL))
> > + return 0;
> > + }
> > +
> > + /* if we get here, CEU has not reset properly */
> > + return -EIO;
> > +}
> > +
> > +/* CEU Capture Operations */
>
> Just curious, why have you replaced the block comments by single-line comments
> ? I pointed out that the format was wrong as you started them with /** and
> they were not kerneldoc, but I have nothing against splitting the code in
> sections with headers such as
>
> /* --------------------------------------------------------------------------
> * CEU Capture Operations
> */
>
> as I do so routinely in my drivers. If that's your preferred style and you
> thought I asked for a change you can switch back, if you prefer single-line
> comments that's fine with me too.

Yes I borrowed that commenting style from other Renesas drivers you
wrote, so I went for it for consistency.

I recently read about some discussions on block comments, when Mauro
was trying to replace /***...***/ block comments with a script, and
I had the feeling there's not that much love for block comments around
here, and I also find them a bit invasive.

I used the
/* --- Code section --- */
style in the past which I find is a good balance between
intrusiveness and noticeability but I don't want to introduce
yet-another-comment-style so I went for single line and that's it.

>
> [snip]
>
> > +/*
> > + * ceu_calc_plane_sizes() - Fill per-plane 'struct v4l2_plane_pix_format'
> > + * information according to the currently configured
> > + * pixel format.
> > + * @ceu_device: CEU device.
> > + * @ceu_fmt: Active image format.
> > + * @pix: Pixel format information (store line width and image sizes)
> > + *
> > + * Returns 0 for success.
> > + */
> > +static int ceu_calc_plane_sizes(struct ceu_device *ceudev,
> > + const struct ceu_fmt *ceu_fmt,
> > + struct v4l2_pix_format_mplane *pix)
> > +{
> > + unsigned int bpl, szimage;
> > +
> > + switch (pix->pixelformat) {
> > + case V4L2_PIX_FMT_YUYV:
> > + pix->num_planes = 1;
> > + bpl = pix->width * ceu_fmt->bpp / 8;
> > + szimage = pix->height * bpl;
> > + ceu_update_plane_sizes(&pix->plane_fmt[0], bpl, szimage);
> > + break;
> > +
> > + case V4L2_PIX_FMT_NV16:
> > + case V4L2_PIX_FMT_NV61:
> > + pix->num_planes = 2;
> > + bpl = pix->width;
> > + szimage = pix->height * pix->width;
> > + ceu_update_plane_sizes(&pix->plane_fmt[0], bpl, szimage);
> > + ceu_update_plane_sizes(&pix->plane_fmt[1], bpl, szimage);
> > + break;
> > +
> > + case V4L2_PIX_FMT_NV12:
> > + case V4L2_PIX_FMT_NV21:
> > + pix->num_planes = 2;
> > + bpl = pix->width;
> > + szimage = pix->height * pix->width;
> > + ceu_update_plane_sizes(&pix->plane_fmt[0], bpl, szimage);
> > + ceu_update_plane_sizes(&pix->plane_fmt[1], bpl, szimage / 2);
> > + break;
> > +
> > + default:
> > + pix->num_planes = 0;
> > + dev_err(ceudev->dev,
> > + "Format 0x%x not supported\n", pix->pixelformat);
> > + return -EINVAL;
>
> I think you can remove the default case as ceu_try_fmt() should have validated
> the format already. The compiler will then likely warn so you need to keep a
> default cause, but it will never be hit, so it can default to any format you
> want. The function can then be turned into a void.

Yes, that was only to silence the compiler actually...

>
> > + }
> > +
> > + return 0;
> > +}
>
> [snip]
>
> > +/*
> > + * ceu_set_default_fmt() - Apply default NV16 memory output format with VGA
> > + * sizes.
> > + */
> > +static int ceu_set_default_fmt(struct ceu_device *ceudev)
> > +{
> > + struct v4l2_format v4l2_fmt = {
> > + .type = V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE,
> > + .fmt.pix_mp = {
> > + .width = VGA_WIDTH,
> > + .height = VGA_HEIGHT,
> > + .field = V4L2_FIELD_NONE,
> > + .pixelformat = V4L2_PIX_FMT_NV16,
> > + .num_planes = 2,
> > + .plane_fmt = {
> > + [0] = {
> > + .sizeimage = VGA_WIDTH * VGA_HEIGHT * 2,
> > + .bytesperline = VGA_WIDTH * 2,
> > + },
> > + [1] = {
> > + .sizeimage = VGA_WIDTH * VGA_HEIGHT * 2,
> > + .bytesperline = VGA_WIDTH * 2,
> > + },
> > + },
> > + },
> > + };
> > +
> > + ceu_try_fmt(ceudev, &v4l2_fmt);
>
> You've removed the error check here. ceu_try_fmt() shouldn't fail, but it
> calls a sensor driver subdev operation over which you have no control. It's up
> to you, but if you decide to ignore errors, I would turn this function into
> void.
>
> I know I've asked in my review of v1 for the error check to be removed, but I
> think I had missed the fact that a subdev operation was called.
>

Yes, and I blindly changed it, so my bad as well..

> > + ceudev->v4l2_pix = v4l2_fmt.fmt.pix_mp;
> > +
> > + return 0;
> > +}
>
> [snip]
>
>
>
> [snip]
>

I have now fixed all of the above comments, and will send v3 shortly!

Thanks
j

> --
> Regards,
>
> Laurent Pinchart
>