Re: [PATCH v3 1/6] media: mt9p031: Read back the real clock rate

Sakari Ailus
2021-07-05T07:13:54Z

Hi Enrico,

On Fri, Jul 02, 2021 at 11:59:17AM +0200, Stefan Riedmueller wrote:
> From: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
>
> The real and requested clock can differ and because it is used to
> calculate PLL values, the real clock rate should be read.

Do you have a system where this happens? That suggests there's a wrong
value in DT.

The preference nowadays is to rely on assigned-clock-rates, even though
it's inherently somewhat unreliable, just as clk_set_rate(). This is an
existing driver though. The old ones could be kept for compatibility with
older DT binaries.

>
> Signed-off-by: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
> Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> ---
> drivers/media/i2c/mt9p031.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/media/i2c/mt9p031.c b/drivers/media/i2c/mt9p031.c
> index 77567341ec98..3eaaa8d44523 100644
> --- a/drivers/media/i2c/mt9p031.c
> +++ b/drivers/media/i2c/mt9p031.c
> @@ -255,6 +255,7 @@ static int mt9p031_clk_setup(struct mt9p031 *mt9p031)
>
> struct i2c_client *client = v4l2_get_subdevdata(&mt9p031->subdev);
> struct mt9p031_platform_data *pdata = mt9p031->pdata;
> + unsigned long ext_freq;
> int ret;
>
> mt9p031->clk = devm_clk_get(&client->dev, NULL);
> @@ -265,13 +266,15 @@ static int mt9p031_clk_setup(struct mt9p031 *mt9p031)
> if (ret < 0)
> return ret;
>
> + ext_freq = clk_get_rate(mt9p031->clk);
> +
> /* If the external clock frequency is out of bounds for the PLL use the
> * pixel clock divider only and disable the PLL.
> */
> - if (pdata->ext_freq > limits.ext_clock_max) {
> + if (ext_freq > limits.ext_clock_max) {
> unsigned int div;
>
> - div = DIV_ROUND_UP(pdata->ext_freq, pdata->target_freq);
> + div = DIV_ROUND_UP(ext_freq, pdata->target_freq);
> div = roundup_pow_of_two(div) / 2;
>
> mt9p031->clk_div = min_t(unsigned int, div, 64);
> @@ -280,7 +283,7 @@ static int mt9p031_clk_setup(struct mt9p031 *mt9p031)
> return 0;
> }
>
> - mt9p031->pll.ext_clock = pdata->ext_freq;
> + mt9p031->pll.ext_clock = ext_freq;
> mt9p031->pll.pix_clock = pdata->target_freq;
> mt9p031->use_pll = true;
>

--
Kind regards,

Sakari Ailus