[PATCH v2 3/4] thermal: armada: add support for CP110

Wed Dec 13 00:38:48 PST 2017

Hi Gregory,

On Mon, Dec 11, 2017 at 06:02:49PM +0100, Gregory CLEMENT wrote:
>  On lun., déc. 11 2017, Baruch Siach <baruch at tkos.co.il> wrote:
> > On Mon, Dec 11, 2017 at 04:09:32PM +0100, Miquel RAYNAL wrote:
> >> On Sun,  3 Dec 2017 13:11:23 +0200
> >> Baruch Siach <baruch at tkos.co.il> wrote:
> >> 
> >> > The CP110 component is integrated in the Armada 8k and 7k lines of
> >> > processors.
> >> > 
> >> > This patch also adds an option of offset to the MSB of the control
> >> > register. The existing DT binding for Armada 38x refers to a single
> >> > 32 bit control register. It turns out that this is actually only the
> >> > MSB of the control area. Changing the binding to fix that would break
> >> > existing DT files, so the Armada 38x binding is left as is.
> >> > 
> >> > The new CP110 binding increases the size of the control area to 64
> >> > bits, thus moving the MSB to offset 4.
> >> > 
> >> > Signed-off-by: Baruch Siach <baruch at tkos.co.il>
> >> > ---
> >> > v2: No change
> >> > ---
> >> >  drivers/thermal/armada_thermal.c | 24 ++++++++++++++++++++++--
> >> >  1 file changed, 22 insertions(+), 2 deletions(-)
> >> > 
> >> > diff --git a/drivers/thermal/armada_thermal.c
> >> > b/drivers/thermal/armada_thermal.c index 0eb82097571f..59b75f63945d
> >> > 100644 --- a/drivers/thermal/armada_thermal.c
> >> > +++ b/drivers/thermal/armada_thermal.c
> >> > @@ -73,6 +73,7 @@ struct armada_thermal_data {
> >> >  	unsigned int temp_shift;
> >> >  	unsigned int temp_mask;
> >> >  	unsigned int is_valid_shift;
> >> > +	unsigned int control_msb_offset;
> >> >  };
> >> >  
> >> >  static void armadaxp_init_sensor(struct platform_device *pdev,
> >> > @@ -142,12 +143,14 @@ static void armada375_init_sensor(struct
> >> > platform_device *pdev, static void armada380_init_sensor(struct
> >> > platform_device *pdev, struct armada_thermal_priv *priv)
> >> >  {
> >> > -	unsigned long reg = readl_relaxed(priv->control);
> >> > +	void __iomem *control_msb =
> >> > +		priv->control + priv->data->control_msb_offset;
> >> > +	unsigned long reg = readl_relaxed(control_msb);
> >> >  
> >> >  	/* Reset hardware once */
> >> >  	if (!(reg & A380_HW_RESET)) {
> >> >  		reg |= A380_HW_RESET;
> >> > -		writel(reg, priv->control);
> >> > +		writel(reg, control_msb);
> >> >  		mdelay(10);
> >> >  	}
> >> >  }
> >> > @@ -266,6 +269,19 @@ static const struct armada_thermal_data
> >> > armada_ap806_data = { .signed_sample = true,
> >> >  };
> >> >  
> >> > +static const struct armada_thermal_data armada_cp110_data = {
> >> > +	.is_valid = armada_is_valid,
> >> > +	.init_sensor = armada380_init_sensor,
> >> 
> >> I see the initialization for CP110 thermal IP is close to
> >> Armada-380's, but, as you point it in the commit log it is still
> >> different.
> >> 
> >> I don't know what is the best way to handle this but until now each
> >> new compatible had his own ->init_sensor function, shouldn't we do
> >> the same here as changes are requested? This would naturally avoid the
> >> situation with Armada-380 bindings.
> >
> > I'm not sure I understand your suggestion.
> >
> > There is no difference between the CP110 and the Armada 38x, as far as I can 
> > see. The only quirk is that the existing Armada 38x DT binding is wrong I that 
> > the 'reg' property references the control MSB, while leaving the LSB
> > out. We
> 
> Well I would not say it was wrong but more incomplete :)
> 
> > can't change the Armada 38x binding without breaking existing DTs. The 
> > 'control_msb_offset' field that this patch adds allows correct binding for 
> > CP110, while keeping compatibility with the existing Armada 38x
> > binding.
> 
> I am not against adding a new compatible string for CP110 but ot be
> honest the new binding for CP110 does not bring anything as you don't
> use at all the LSB register.

We don't use the LSB yet in mainline driver. But the vendor kernel uses it to 
"change temperature band gap circuit curve" (quoting vendor kernel commit 
4ff2d8a7d3 log). Chances are that we want to do this as well. But said commit 
changed the DT binding in an incompatible way. We can't do that, and we both 
agree on that.

> Actually, if on Armada 375 we initially mapped the LSB register it was
> to support an very early release of the SoC (stepping Z) and only for
> resetting its value. So I guess you started to write the AP860 part
> based on the Armada 375 and then found that we could map a more complete
> range of the registers.
> 
> > How would a separate init_sensor routine improve things?
> 
> So yes please do it, thanks to this you won't have to add the
> control_msb_offset member and can use a clean function. Moreover if in
> the future we see some usefulness for this LSB register then we could use
> the new compatible for the Armada 38x.

There are two separate issues here:

  1. DT binding

  2. init_sensor callback implementation

We both agree on #1. The A38x and CP110 need separate compatible strings. In 
case we want to access the LSB control register on Armada 38x, we will need 
yet another compatible string (marvell,armada380-v2-thermal maybe?).

As for #2, I'm all for sharing as much code as possible. I find the vendor 
kernel approach of duplicating the init routines[1] unhelpful as it violates 
the DRY principle. The differences between armada380_init_sensor() and 
cp110_init_sensor() are minor. In my opinion, these differences should be 
expressed explicitly in the armada_thermal_data, in a similar way to my 
suggested control_msb_offset field. The vendor code hides these differences in 
slight variations of duplicated code.

What is the advantage of a separate init routine?

baruch

[1] https://github.com/MarvellEmbeddedProcessors/linux-marvell/blob/linux-4.4.52-armada-17.10/drivers/thermal/armada_thermal.c

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