On 05/11/18 11:59, Jacopo Mondi wrote:
> Since commit (015060cb "media: rcar-vin: enable field toggle after a set
> number of lines for Gen3) the VIN generates an internal field signal
> toggle after a fixed number of received lines, and uses the internal
> field signal to drive capture operations. When capturing from digital
> input, using FTEH driven field signal toggling messes up the received
> image sizes. Fall back to use FTEV driven signal toggling when capturing
> from digital input.
>
> As explained in the comment, this disables buffer overflow protection
> for digital input capture, for which the FOE overflow might be used in
> future.
I don't know the details of the hardware, but this sounds dangerous.
You should know that with HDMI input it is perfectly possible that you get
more data than you should. I.e. instead of 1080 lines (assuming full HD)
you might get more lines. This happens if the vertical sync is missed due
to pin bounce when connecting a source.
Other reasons for this are flaky signals, bad clocks, etc.
It's rare, but it really happens.
A good DMA engine will refuse to write more than fits in the buffer.
If you disable that, then you will get overflows eventually.
The reality with HDMI input is that you should never assume clean valid
data. You do not control the source and it can send anything it likes.
>
> Signed-off-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
> ---
> drivers/media/platform/rcar-vin/rcar-dma.c | 18 +++++++++++++++++-
> 1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/platform/rcar-vin/rcar-dma.c b/drivers/media/platform/rcar-vin/rcar-dma.c
> index ea7a120..8dc3455 100644
> --- a/drivers/media/platform/rcar-vin/rcar-dma.c
> +++ b/drivers/media/platform/rcar-vin/rcar-dma.c
> @@ -685,11 +685,27 @@ static int rvin_setup(struct rvin_dev *vin)
> break;
> }
>
> - if (vin->info->model == RCAR_GEN3) {
> + if (vin->info->model == RCAR_GEN3 &&
> + vin->mbus_cfg.type == V4L2_MBUS_CSI2) {
> /* Enable HSYNC Field Toggle mode after height HSYNC inputs. */
> lines = vin->format.height / (halfsize ? 2 : 1);
> dmr2 = VNDMR2_FTEH | VNDMR2_HLV(lines);
> vin_dbg(vin, "Field Toogle after %u lines\n", lines);
Typo: Toogle -> Toggle
> + } else if (vin->info->model == RCAR_GEN3 &&
> + vin->mbus_cfg.type == V4L2_MBUS_PARALLEL) {
> + /*
> + * FIXME
> + * Section 26.3.17 specifies that for digital input there's no
> + * need to program FTEH or FTEV to generate internal
> + * field toggle signal to driver capture. Although when
> + * running on GEN3 with digital input no EFE interrupt is ever
> + * generated, and we need to rely on FTEV driven field signal
> + * toggling, as using FTEH as in the CSI-2 case, messes up
> + * the output image size. This implies no protection
> + * against buffer overflow is in place for Gen3 digital input
> + * capture.
> + */
> + dmr2 = VNDMR2_FTEV;
> } else {
> /* Enable VSYNC Field Toogle mode after one VSYNC input. */
Ditto. Search and replace?
> dmr2 = VNDMR2_FTEV | VNDMR2_VLV(1);
>
Regards,
Hans
