Re: [PATCH] media: xilinx: vtc: Dynamically calculate pixel clock

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

CC'ing Tomi who is working on Xilinx V4L2 drivers.

On Wed, Jul 29, 2026 at 03:48:08PM +0530, Rajesh Gugulothu wrote:
> This update enables the vtc to set the pixel clock based on the
> specified timing parameters. A new fps field is added to struct
> xvtc_config and the pixel rate is computed as fps * hsize * vsize.
> After setting the rate, the actual clock rate is read back and a
> warning is emitted if it deviates beyond a small tolerance.
> 
> The pixel rate is computed in unsigned long arithmetic to avoid a 32-bit
> overflow in the fps * hsize * vsize product.
> 
> Signed-off-by: Rajesh Gugulothu <rajesh.gugulothu@amd.com>
> ---
>  drivers/media/platform/xilinx/xilinx-vtc.c | 19 +++++++++++++++++++
>  drivers/media/platform/xilinx/xilinx-vtc.h |  1 +
>  2 files changed, 20 insertions(+)
> 
> diff --git a/drivers/media/platform/xilinx/xilinx-vtc.c b/drivers/media/platform/xilinx/xilinx-vtc.c
> index 92fec7bb4..695eb2a46 100644
> --- a/drivers/media/platform/xilinx/xilinx-vtc.c
> +++ b/drivers/media/platform/xilinx/xilinx-vtc.c
> @@ -141,6 +141,9 @@
>  
>  #define XVTC_GENERATOR_GLOBAL_DELAY		0x0104
>  
> +/* Value of 1 = .01% */
> +#define XVTC_CLK_MAX_PCT_ERR			1
> +
>  /**
>   * struct xvtc_device - Xilinx Video Timing Controller device structure
>   * @xvip: Xilinx Video IP device
> @@ -175,10 +178,26 @@ int xvtc_generator_start(struct xvtc_device *xvtc,
>  			 const struct xvtc_config *config)
>  {
>  	int ret;
> +	unsigned long s_rate;
> +	unsigned long g_rate;
> +	unsigned long clk_err;
>  
>  	if (!xvtc->has_generator)
>  		return -ENXIO;
>  
> +	s_rate = (unsigned long)config->fps * config->hsize * config->vsize;
> +	ret = clk_set_rate(xvtc->xvip.clk, s_rate);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* Verify that the clock is within a reasonable tolerance. */
> +	g_rate = clk_get_rate(xvtc->xvip.clk);
> +	clk_err = (abs(g_rate - s_rate) * 10000) / (s_rate);
> +	if (clk_err > XVTC_CLK_MAX_PCT_ERR)
> +		dev_warn(xvtc->xvip.dev,
> +			 "Failed to set clk rate: %lu, actual rate: %lu\n",
> +			 s_rate, g_rate);
> +
>  	ret = clk_prepare_enable(xvtc->xvip.clk);
>  	if (ret < 0)
>  		return ret;
> diff --git a/drivers/media/platform/xilinx/xilinx-vtc.h b/drivers/media/platform/xilinx/xilinx-vtc.h
> index 855845911..0f360ed55 100644
> --- a/drivers/media/platform/xilinx/xilinx-vtc.h
> +++ b/drivers/media/platform/xilinx/xilinx-vtc.h
> @@ -27,6 +27,7 @@ struct xvtc_config {
>  	unsigned int vsync_start;
>  	unsigned int vsync_end;
>  	unsigned int vsize;
> +	unsigned int fps;
>  };
>  
>  struct xvtc_device *xvtc_of_get(struct device_node *np);

-- 
Regards,

Laurent Pinchart