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

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Message-ID: <0c704fea-f2a6-2cec-8741-d322acf6afd5@st.com>
Date:   Mon, 11 May 2020 14:47:09 +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 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.

Regards,
Christophe Kerello.

> 
> Thanks,
> Miquèl
>