Re: [PATCH v3 27/31] net: can: mscan: add common clock support for mpc512x

[Gerhard Sittig <gsi@denx.de>]

[ adjusted devtree to use the vger address ]

On Mon, Jul 22, 2013 at 15:04 +0200, Marc Kleine-Budde wrote:
> 
> On 07/22/2013 02:14 PM, Gerhard Sittig wrote:
> > implement a .get_clock() callback for the MPC512x platform which uses
> > the common clock infrastructure (eliminating direct access to the clock
> > control registers from within the CAN network driver), and provide the
> > corresponding .put_clock() callback to release resources after use
> > 
> > keep the previous implementation of MPC512x support in place during
> > migration, since common clock support is optional
> > 
> > this change is neutral to the MPC5200 platform
> > 
> > Signed-off-by: Gerhard Sittig <gsi@denx.de>
> > ---
> >  drivers/net/can/mscan/mpc5xxx_can.c |  169 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 169 insertions(+)
> > 
> > diff --git a/drivers/net/can/mscan/mpc5xxx_can.c b/drivers/net/can/mscan/mpc5xxx_can.c
> > index e59b3a3..4897929 100644
> > --- a/drivers/net/can/mscan/mpc5xxx_can.c
> > +++ b/drivers/net/can/mscan/mpc5xxx_can.c
> > @@ -109,6 +109,167 @@ static u32 mpc52xx_can_get_clock(struct platform_device *ofdev,
> >  #endif /* CONFIG_PPC_MPC52xx */
> >  
> >  #ifdef CONFIG_PPC_MPC512x
> > +
> > +#if IS_ENABLED(CONFIG_COMMON_CLK)
> > +
> > +static u32 mpc512x_can_get_clock(struct platform_device *ofdev,
> > +				 const char *clock_source, int *mscan_clksrc)
> > +{
> > +	struct device_node *np;
> > +	u32 clockdiv;
> > +	enum {
> > +		CLK_FROM_AUTO,
> > +		CLK_FROM_IPS,
> > +		CLK_FROM_SYS,
> > +		CLK_FROM_REF,
> > +	} clk_from;
> > +	struct clk *clk_in, *clk_can;
> > +	unsigned long freq_calc;
> > +	struct mscan_priv *priv;
> > +
> > +	/* the caller passed in the clock source spec that was read from
> > +	 * the device tree, get the optional clock divider as well
> > +	 */
> > +	np = ofdev->dev.of_node;
> > +	clockdiv = 1;
> > +	of_property_read_u32(np, "fsl,mscan-clock-divider", &clockdiv);
> > +	dev_dbg(&ofdev->dev, "device tree specs: clk src[%s] div[%d]\n",
> > +		clock_source ? clock_source : "<NULL>", clockdiv);
> > +
> > +	/* when clock-source is 'ip', the CANCTL1[CLKSRC] bit needs to
> > +	 * get set, and the 'ips' clock is the input to the MSCAN
> > +	 * component
> > +	 *
> > +	 * for clock-source values of 'ref' or 'sys' the CANCTL1[CLKSRC]
> > +	 * bit needs to get cleared, an optional clock-divider may have
> > +	 * been specified (the default value is 1), the appropriate
> > +	 * MSCAN related MCLK is the input to the MSCAN component
> > +	 *
> > +	 * in the absence of a clock-source spec, first an optimal clock
> > +	 * gets determined based on the 'sys' clock, if that fails the
> > +	 * 'ref' clock is used
> > +	 */
> > +	clk_from = CLK_FROM_AUTO;
> > +	if (clock_source) {
> > +		/* interpret the device tree's spec for the clock source */
> > +		if (!strcmp(clock_source, "ip"))
> > +			clk_from = CLK_FROM_IPS;
> > +		else if (!strcmp(clock_source, "sys"))
> > +			clk_from = CLK_FROM_SYS;
> > +		else if (!strcmp(clock_source, "ref"))
> > +			clk_from = CLK_FROM_REF;
> > +		else
> > +			goto err_invalid;
> > +		dev_dbg(&ofdev->dev, "got a clk source spec[%d]\n", clk_from);
> > +	}
> > +	if (clk_from == CLK_FROM_AUTO) {
> > +		/* no spec so far, try the 'sys' clock; round to the
> > +		 * next MHz and see if we can get a multiple of 16MHz
> > +		 */
> > +		dev_dbg(&ofdev->dev, "no clk source spec, trying SYS\n");
> > +		clk_in = devm_clk_get(&ofdev->dev, "sys");
> > +		if (IS_ERR(clk_in))
> > +			goto err_notavail;
> > +		freq_calc = clk_get_rate(clk_in);
> > +		freq_calc +=  499999;
> > +		freq_calc /= 1000000;
> > +		freq_calc *= 1000000;
> > +		if ((freq_calc % 16000000) == 0) {
> > +			clk_from = CLK_FROM_SYS;
> > +			clockdiv = freq_calc / 16000000;
> > +			dev_dbg(&ofdev->dev,
> > +				"clk fit, sys[%lu] div[%d] freq[%lu]\n",
> > +				freq_calc, clockdiv, freq_calc / clockdiv);
> > +		}
> > +	}
> > +	if (clk_from == CLK_FROM_AUTO) {
> > +		/* no spec so far, use the 'ref' clock */
> > +		dev_dbg(&ofdev->dev, "no clk source spec, trying REF\n");
> > +		clk_in = devm_clk_get(&ofdev->dev, "ref");
> > +		if (IS_ERR(clk_in))
> > +			goto err_notavail;
> > +		clk_from = CLK_FROM_REF;
> > +		freq_calc = clk_get_rate(clk_in);
> > +		dev_dbg(&ofdev->dev,
> > +			"clk fit, ref[%lu] (no div) freq[%lu]\n",
> > +			freq_calc, freq_calc);
> > +	}
> > +
> > +	/* select IPS or MCLK as the MSCAN input (returned to the caller),
> > +	 * setup the MCLK mux source and rate if applicable, apply the
> > +	 * optionally specified or derived above divider, and determine
> > +	 * the actual resulting clock rate to return to the caller
> > +	 */
> > +	switch (clk_from) {
> > +	case CLK_FROM_IPS:
> > +		clk_can = devm_clk_get(&ofdev->dev, "ips");
> > +		if (IS_ERR(clk_can))
> > +			goto err_notavail;
> > +		if (clk_prepare(clk_can)) {
> 
> I would just call prepare_enable in the main mscan driver, then we don't
> need a special "clock is prepared but not enabled" contract.

Yes, I addressed this concern (although differently after
learning more from a local test setup), see the other reply for
the CAN driver adjustment for clock API use.

> 
> > +			devm_clk_put(&ofdev->dev, clk_can);
> 
> not needed, as this driver instance will fail, doesn't it?

This is discussed in the other subthread as well.  The only
remaining question is how many of them to remove, before I'll
update the series.

> > +			goto err_notavail;
> > +		}
> > +		priv = netdev_priv(dev_get_drvdata(&ofdev->dev));
> > +		priv->clk_can = clk_can;
> > +		freq_calc = clk_get_rate(clk_can);
> > +		*mscan_clksrc = MSCAN_CLKSRC_IPS;
> > +		dev_dbg(&ofdev->dev, "clk from IPS, clksrc[%d] freq[%lu]\n",
> > +			*mscan_clksrc, freq_calc);
> > +		break;
> > +	case CLK_FROM_SYS:
> > +	case CLK_FROM_REF:
> > +		clk_can = devm_clk_get(&ofdev->dev, "mclk");
> > +		if (IS_ERR(clk_can))
> > +			goto err_notavail;
> > +		if (clk_prepare(clk_can)) {
> > +			devm_clk_put(&ofdev->dev, clk_can);
> 
> same here
> 
> > +			goto err_notavail;
> > +		}
> > +		priv = netdev_priv(dev_get_drvdata(&ofdev->dev));
> > +		priv->clk_can = clk_can;
> > +		if (clk_from == CLK_FROM_SYS)
> > +			clk_in = devm_clk_get(&ofdev->dev, "sys");
> > +		if (clk_from == CLK_FROM_REF)
> > +			clk_in = devm_clk_get(&ofdev->dev, "ref");
> > +		if (IS_ERR(clk_in))
> > +			goto err_notavail;
> > +		clk_set_parent(clk_can, clk_in);
> > +		freq_calc = clk_get_rate(clk_in);
> > +		freq_calc /= clockdiv;
> > +		clk_set_rate(clk_can, freq_calc);
> > +		freq_calc = clk_get_rate(clk_can);
> > +		*mscan_clksrc = MSCAN_CLKSRC_BUS;
> > +		dev_dbg(&ofdev->dev, "clk from MCLK, clksrc[%d] freq[%lu]\n",
> > +			*mscan_clksrc, freq_calc);
> > +		break;
> > +	default:
> > +		goto err_invalid;
> > +	}
> > +
> > +	return freq_calc;
> > +
> > +err_invalid:
> > +	dev_err(&ofdev->dev, "invalid clock source specification\n");
> > +	return 0;
> 
> return 0 in case of error? Please add a comment what this 0 means here.

The .get_clock() callback is supposed to return the resulting
rate after the clock source was determined and the clock subtree
was setup.  It wasn't (explicitly) documented before (in the
non-common-clock case), so I did not bother to comment it in the
parallel common-clock case.

But it's true that returning zero in the error case may be
unexpected, and I will add a comment in v4 (in all the
.get_clock() implementations).

> > +
> > +err_notavail:
> > +	dev_err(&ofdev->dev, "cannot acquire or setup clock source\n");
> > +	return 0;
> > +}
> > +
> > +static void mpc512x_can_put_clock(struct platform_device *ofdev)
> > +{
> > +	struct mscan_priv *priv;
> > +
> > +	priv = netdev_priv(dev_get_drvdata(&ofdev->dev));
> > +	if (priv->clk_can) {
> > +		clk_unprepare(priv->clk_can);
> > +		devm_clk_put(&ofdev->dev, priv->clk_can);
> 
> devm_clk_put can be removed, it's called automatically.
> 
> > +	}
> > +}
> > +
> > +#else	/* COMMON_CLK */
> > +
> >  struct mpc512x_clockctl {
> >  	u32 spmr;		/* System PLL Mode Reg */
> >  	u32 sccr[2];		/* System Clk Ctrl Reg 1 & 2 */
> > @@ -239,12 +400,18 @@ exit_put:
> >  	of_node_put(np_clock);
> >  	return freq;
> >  }
> > +
> > +#define mpc512x_can_put_clock NULL
> > +
> > +#endif	/* COMMON_CLK */
> > +
> >  #else /* !CONFIG_PPC_MPC512x */
> >  static u32 mpc512x_can_get_clock(struct platform_device *ofdev,
> >  				 const char *clock_name, int *mscan_clksrc)
> >  {
> >  	return 0;
> >  }
> > +#define mpc512x_can_put_clock NULL
> >  #endif /* CONFIG_PPC_MPC512x */
> >  
> >  static const struct of_device_id mpc5xxx_can_table[];
> > @@ -386,11 +553,13 @@ static int mpc5xxx_can_resume(struct platform_device *ofdev)
> >  static const struct mpc5xxx_can_data mpc5200_can_data = {
> >  	.type = MSCAN_TYPE_MPC5200,
> >  	.get_clock = mpc52xx_can_get_clock,
> > +	/* .put_clock not applicable */
> >  };
> >  
> >  static const struct mpc5xxx_can_data mpc5121_can_data = {
> >  	.type = MSCAN_TYPE_MPC5121,
> >  	.get_clock = mpc512x_can_get_clock,
> > +	.put_clock = mpc512x_can_put_clock,
> >  };
> >  
> >  static const struct of_device_id mpc5xxx_can_table[] = {
> > 
> 
> Marc

Thank you for the fast and detailled review.  It's very much
appreciated.


virtually yours
Gerhard Sittig
-- 
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