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

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Date:   Mon, 11 May 2020 16:19:47 +0200
From:   Christophe Kerello <christophe.kerello@...com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
CC:     <richard@....at>, <vigneshr@...com>, <robh+dt@...nel.org>,
        <mark.rutland@....com>, <gregkh@...uxfoundation.org>,
        <boris.brezillon@...labora.com>, <linux-mtd@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <devicetree@...r.kernel.org>, <marex@...x.de>
Subject: Re: [PATCH v4 10/10] mtd: rawnand: stm32_fmc2: get resources from
 parent node

Hi Miquel,

On 5/11/20 2:58 PM, Miquel Raynal wrote:
> Hi Christophe,
> 
> Christophe Kerello <christophe.kerello@...com> wrote on Mon, 11 May
> 2020 14:47:09 +0200:
> 
>> Hi Miquel,
>>
>> On 5/11/20 1:59 PM, Miquel Raynal wrote:
>>> Hi Christophe,
>>>
>>> Christophe Kerello <christophe.kerello@...com> 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@...com> 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@...com>
>>>>>> ---
>>>>>
>>>>> [...]
>>>>>     >>>> +
>>>>>> +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.
> 
> I had something slightly different in mind: what about setting a
> default value to this field as being the controller's device itself.
> This way, once it is set to either the parent device or the device
> itself, you can use it "blindly" in your devm_clk_get/regmap_init calls?
> 

I will try to explain what I have in mind.

I will add a new field in the structure of the controller (not called 
dev_parent but cdev)
struct device *cdev;

Then, at probe time, this field will be assigned:
nfc->cdev = of_device_is_compatible(dev->parent->of_node, "bla bla") : 
dev->parent ? dev;

For the clock, it will be
nfc->clk = devm_clk_get(nfc->cdev, NULL);

For the register base, I need to replace:
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
mmio = devm_ioremap_resource(dev, res);
if (IS_ERR(mmio))
	return PTR_ERR(mmio);

nfc->regmap = devm_regmap_init_mmio(dev, mmio, &stm32_fmc2_regmap_cfg);
if (IS_ERR(nfc->regmap))
	return PTR_ERR(nfc->regmap);

nfc->io_phys_addr = res->start;

With:

ret = of_address_to_resource(nfc->cdev->of_node, 0, &res);
if (ret)
	return ret;

nfc->io_phys_addr = res.start;

nfc->regmap = device_node_to_regmap(nfc->cdev->of_node);
if (IS_ERR(nfc->regmap))
	return PTR_ERR(nfc->regmap);

I expect that you were thinking about something like this proposal.

Regards,
Christophe Kerello.