Re: [PATCH v4 10/10] mtd: rawnand: stm32_fmc2: get resources from parent node

[Christophe Kerello]

Hi Miquel,

On 5/11/20 1:59 PM, Miquel Raynal wrote:
> Hi Christophe,
>
> Christophe Kerello <christophe.kerello@xxxxxx> wrote on Mon, 11 May
> 2020 12:21:03 +0200:
>
> > Hi Miquel,
> >
> > On 5/11/20 11:18 AM, Miquel Raynal wrote:
> > > Hi Christophe,
> > >
> > > Christophe Kerello <christophe.kerello@xxxxxx> wrote on Wed, 6 May 2020
> > > 11:11:19 +0200:
> > >    
> > > > FMC2 EBI support has been added. Common resources (registers base
> > > > and clock) are now shared between the 2 drivers. It means that the
> > > > common resources should now be found in the parent device when EBI
> > > > node is available.
> > > >
> > > > Signed-off-by: Christophe Kerello <christophe.kerello@xxxxxx>
> > > > ---
> > >
> > > [...]
> > >    
> > > > +
> > > > +static bool stm32_fmc2_nfc_check_for_parent(struct platform_device *pdev)
> > > > +{
> > > > +	u32 i;
> > > > +	int nb_resources = 0;
> > > > +
> > > > +	/* Count the number of resources in reg property */
> > > > +	for (i = 0; i < pdev->num_resources; i++) {
> > > > +		struct resource *res = &pdev->resource[i];
> > > > +
> > > > +		if (resource_type(res) == IORESOURCE_MEM)
> > > > +			nb_resources++;
> > > > +	}
> > > > +
> > > > +	/* Each CS needs 3 resources defined (data, cmd and addr) */
> > > > +	if (nb_resources % 3)
> > > > +		return false;
> > > > +
> > > > +	return true;
> > > > +}
> > >
> > > This function looks fragile. Why not just checking the compatible
> > > string of the parent node?
> > >    
> >
> > Yes, it is another way to check that we have an EBI parent node.
> >
> > In this implementation, I was checking the number of reg tuples.
> > In case we have 6, it means that the register base address is defined in the parent node (EBI node).
> > In case we have 7, it means that the register base address is defined in the current node (NFC node).
>
> Yes, I understand what you are doing, but I kind of dislike the logic.
> Relying on the number of reg tuples is something that can be done (I
> used it myself one time), but I think this is more a hack that you do
> when you have no other way to differentiate. I guess the proper way
> would be to look at the parent's compatible. If it matches what you
> expect, then you can store the dev->of_node->parent->dev somewhere in
> your controller's structure and then use it to initialize the clock and
> regmap. This way you don't have to move anything else in the probe path.

OK, I will check the compatible string of the parent device using 
of_device_is_compatible API in v5.
In case of the parent is found, I will add it in the structure of the 
controller (dev_parent).
I will rely on this field only to get the common resources (the register 
base address and the clock) in the NFC node or in the EBI node.

Regards,
Christophe Kerello.

> Thanks,
> MiquÃl