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From: "Stefan Riedmüller" <S.Riedmueller@phytec.de>
To: "sakari.ailus@linux.intel.com" <sakari.ailus@linux.intel.com>
Cc: "mchehab@kernel.org" <mchehab@kernel.org>,
	"laurent.pinchart@ideasonboard.com" 
	<laurent.pinchart@ideasonboard.com>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"robh+dt@kernel.org" <robh+dt@kernel.org>,
	"enrico.scholz@sigma-chemnitz.de"
	<enrico.scholz@sigma-chemnitz.de>
Subject: Re: [PATCH v3 1/6] media: mt9p031: Read back the real clock rate
Date: Mon, 5 Jul 2021 07:42:01 +0000	[thread overview]
Message-ID: <a1380e68485ace5125031c1123896355936372d1.camel@phytec.de> (raw)
In-Reply-To: <20210705071343.GR3@paasikivi.fi.intel.com>

Hi Sakari,

On Mon, 2021-07-05 at 10:13 +0300, Sakari Ailus wrote:
> 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 use case here is when the clock is supplied by one of the clock outputs of
a SOC which might not hit the requested frequency exactly due to internal PLL
configuration. So to get a better pixel clock the actual clock rate is read to
calculate the PLL parameters on the sensor. At least that's the idea.

Regards,
Stefan

> 
> 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;
> >  

  reply	other threads:[~2021-07-05  7:42 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-02  9:59 [PATCH v3 0/6] media: mt9p031: Read back the real clock rate Stefan Riedmueller
2021-07-02  9:59 ` [PATCH v3 1/6] " Stefan Riedmueller
2021-07-05  7:13   ` Sakari Ailus
2021-07-05  7:42     ` Stefan Riedmüller [this message]
2021-07-02  9:59 ` [PATCH v3 2/6] media: mt9p031: Make pixel clock polarity configurable by DT Stefan Riedmueller
2021-07-02  9:59 ` [PATCH v3 3/6] dt-bindings: media: mt9p031: Add missing required properties Stefan Riedmueller
2021-07-02 13:15   ` Laurent Pinchart
2021-07-05 15:00     ` Stefan Riedmüller
2021-07-02  9:59 ` [PATCH v3 4/6] dt-bindings: media: mt9p031: add pclk-sample property Stefan Riedmueller
2021-07-02  9:59 ` [PATCH v3 5/6] media: mt9p031: Fix corrupted frame after restarting stream Stefan Riedmueller
2021-07-02  9:59 ` [PATCH v3 6/6] media: mt9p031: Use BIT macro Stefan Riedmueller
2021-07-02 13:13   ` Laurent Pinchart

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