linux-kernel - Re: [PATCH 6/6] media: ov6650: Fix arbitrary selection of master clock rate

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Date:   Fri, 18 Oct 2019 21:11:59 +0200
From:   Janusz Krzysztofik <jmkrzyszt@...il.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] media: ov6650: Fix arbitrary selection of master clock rate

Hi Sakari,

On Friday, October 18, 2019 8:54:19 P.M. CEST Sakari Ailus wrote:
> Hi Janusz,
> 
> On Sun, Oct 13, 2019 at 02:50:50PM +0200, Janusz Krzysztofik wrote:
> > A hardcoded 12 MHz master clock frequency has been assumed since
> > conversion of the driver from soc_camera sensor to a standalone V4L2
> > subdevice by commit 23a52386fabe ("media: ov6650: convert to standalone
> > v4l2 subdevice").  Fix it.
> > 
> > Define a static table of supported master clock rates (fix misnamed
> > symbol while being at it), then use v4l2_clk_get/set_rate() to obtain
> > a clock rate matching one of those supported.  On success, apply
> > respective master clock hardware divisor provided by the matching
> > element of the table.
> > 
> > Signed-off-by: Janusz Krzysztofik <jmkrzyszt@...il.com>
> > ---
> >  drivers/media/i2c/ov6650.c | 64 ++++++++++++++++++++++++++++++++++----
> >  1 file changed, 58 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/media/i2c/ov6650.c b/drivers/media/i2c/ov6650.c
> > index f4723c0b5c70..13fd7c4699b2 100644
> > --- a/drivers/media/i2c/ov6650.c
> > +++ b/drivers/media/i2c/ov6650.c
> > @@ -124,7 +124,7 @@
> >  
> >  #define DEF_AECH		0x4D
> >  
> > -#define CLKRC_6MHz		0x00
> > +#define CLKRC_8MHz		0x00
> >  #define CLKRC_12MHz		0x40
> >  #define CLKRC_16MHz		0x80
> >  #define CLKRC_24MHz		0xc0
> > @@ -201,6 +201,29 @@ struct ov6650 {
> >  	u32 code;
> >  };
> >  
> > +struct ov6650_xclk {
> > +	unsigned long	rate;
> > +	u8		clkrc;
> > +};
> > +
> > +static const struct ov6650_xclk ov6650_xclk[] = {
> > +{
> > +	.rate	= 8000000,
> > +	.clkrc	= CLKRC_8MHz,
> > +},
> > +{
> > +	.rate	= 12000000,
> > +	.clkrc	= CLKRC_12MHz,
> > +},
> > +{
> > +	.rate	= 16000000,
> > +	.clkrc	= CLKRC_16MHz,
> > +},
> > +{
> > +	.rate	= 24000000,
> > +	.clkrc	= CLKRC_24MHz,
> > +},
> > +};
> >  
> >  static u32 ov6650_codes[] = {
> >  	MEDIA_BUS_FMT_YUYV8_2X8,
> > @@ -774,7 +797,7 @@ static int ov6650_reset(struct i2c_client *client)
> >  }
> >  
> >  /* program default register values */
> > -static int ov6650_prog_dflt(struct i2c_client *client)
> > +static int ov6650_prog_dflt(struct i2c_client *client, u8 clkrc)
> >  {
> >  	int ret;
> >  
> > @@ -782,7 +805,7 @@ static int ov6650_prog_dflt(struct i2c_client *client)
> >  
> >  	ret = ov6650_reg_write(client, REG_COMA, 0);	/* ~COMA_RESET */
> >  	if (!ret)
> > -		ret = ov6650_reg_write(client, REG_CLKRC, CLKRC_12MHz);
> > +		ret = ov6650_reg_write(client, REG_CLKRC, clkrc);
> >  	if (!ret)
> >  		ret = ov6650_reg_rmw(client, REG_COMB, 0, COMB_BAND_FILTER);
> >  
> > @@ -793,8 +816,10 @@ static int ov6650_video_probe(struct v4l2_subdev *sd)
> >  {
> >  	struct i2c_client *client = v4l2_get_subdevdata(sd);
> >  	struct ov6650 *priv = to_ov6650(client);
> > -	u8		pidh, pidl, midh, midl;
> > -	int		ret;
> > +	const struct ov6650_xclk *xclk;
> > +	unsigned long rate;
> > +	u8 pidh, pidl, midh, midl;
> > +	int i, ret;
> >  
> >  	priv->clk = v4l2_clk_get(&client->dev, NULL);
> >  	if (IS_ERR(priv->clk)) {
> > @@ -803,6 +828,33 @@ static int ov6650_video_probe(struct v4l2_subdev *sd)
> >  		return ret;
> >  	}
> >  
> > +	rate = v4l2_clk_get_rate(priv->clk);
> > +	for (i = 0; rate && i < ARRAY_SIZE(ov6650_xclk); i++) {
> > +		if (rate != ov6650_xclk[i].rate)
> > +			continue;
> > +
> > +		xclk = &ov6650_xclk[i];
> > +		dev_info(&client->dev, "using host default clock rate %lukHz\n",
> > +			 rate / 1000);
> > +		break;
> > +	}
> 
> xclk is undefined unless it was set in the previous loop. 

Indeed, sorry for that.

> Please initialise
> to to NULL. I can fix that, too, while applying the patch.

OK, please do if you can.

Thanks,
Janusz


> > +	for (i = 0; !xclk && i < ARRAY_SIZE(ov6650_xclk); i++) {
> > +		ret = v4l2_clk_set_rate(priv->clk, ov6650_xclk[i].rate);
> > +		if (ret || v4l2_clk_get_rate(priv->clk) != ov6650_xclk[i].rate)
> > +			continue;
> > +
> > +		xclk = &ov6650_xclk[i];
> > +		dev_info(&client->dev, "using negotiated clock rate %lukHz\n",
> > +			 xclk->rate / 1000);
> > +		break;
> > +	}
> > +	if (!xclk) {
> > +		dev_err(&client->dev, "unable to get supported clock rate\n");
> > +		if (!ret)
> > +			ret = -EINVAL;
> > +		goto eclkput;
> > +	}
> > +
> >  	ret = ov6650_s_power(sd, 1);
> >  	if (ret < 0)
> >  		goto eclkput;
> > @@ -836,7 +888,7 @@ static int ov6650_video_probe(struct v4l2_subdev *sd)
> >  
> >  	ret = ov6650_reset(client);
> >  	if (!ret)
> > -		ret = ov6650_prog_dflt(client);
> > +		ret = ov6650_prog_dflt(client, xclk->clkrc);
> >  	if (!ret) {
> >  		struct v4l2_mbus_framefmt mf = ov6650_def_fmt;
> >  
> 
>