linux-kernel - Re: [RFC PATCH 3/5] mtd: Add support for Hyperbus memory devices

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Message-ID: <acde502c-63fb-e272-d701-4ee63eac4eaa@ti.com>
Date:   Wed, 27 Feb 2019 15:42:27 +0530
From:   Vignesh Raghavendra <vigneshr@...com>
To:     Boris Brezillon <bbrezillon@...nel.org>
CC:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Rob Herring <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        "tudor.ambarus@...rochip.com" <tudor.ambarus@...rochip.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Nori, Sekhar" <nsekhar@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>
Subject: Re: [RFC PATCH 3/5] mtd: Add support for Hyperbus memory devices



On 27/02/19 3:29 PM, Boris Brezillon wrote:
> On Wed, 27 Feb 2019 15:22:19 +0530
> Vignesh Raghavendra <vigneshr@...com> wrote:
> 
>> On 26/02/19 11:46 PM, Sergei Shtylyov wrote:
>>> On 02/19/2019 09:36 AM, Vignesh R (by way of Boris Brezillon <bbrezillon@...nel.org>) wrote:
>>>   
>
[...]
>>>> + */
>>>> +
>>>> +struct hb_device {
>>>> +	struct map_info map;
>>>> +	struct device *dev;
>>>> +	struct device_node *np;
>>>> +	struct mtd_info *mtd;
>>>> +	struct hb_ops *ops;
>>>> +	enum hb_memtype memtype;
>>>> +	bool needs_calib;
>>>> +	bool registered;
>>>> +};
>>>> +
>>>> +/**
>>>> + * struct hb_ops - struct representing custom Hyperbus operations
>>>> + * @read16: read 16 bit of data, usually from register/ID-CFI space
>>>> + * @write16: write 16 bit of data, usually to register/ID-CFI space
>>>> + * copy_from: copy data from flash memory
>>>> + * copy_to: copy data to flash_memory
>>>> + */
>>>> +
>>>> +struct hb_ops {
>>>> +	u16 (*read16)(struct hb_device *hbdev, unsigned long addr);
>>>> +	void (*write16)(struct hb_device *hbdev, unsigned long addr, u16 val);
>>>> +
>>>> +	void (*copy_from)(struct hb_device *hbdev, void *to,
>>>> +			  unsigned long from, ssize_t len);
>>>> +	void (*copy_to)(struct hb_device *dev, unsigned long to,
>>>> +			const void *from, ssize_t len);  
>>>
>>>    ... else these methods won't fly if you need to "massage" the controller
>>> registers inside them...
>>>   
>>
>> If accessing controller register is the only need, wouldn't a private
>> data pointer within struct hb_device be sufficient to hold pointer to
>> controller specific struct?
>>
>> struct hb_device {
>> 	...
>> 	void *priv; /* points to controller's private data */
>> };
>>
>>
>> Or do you see a need for separate structure for the HyperBus controller?
> 
> Sorry to chime in. Just want to share my experience here: properly
> splitting the controller/device representation is always a good thing.
> When it's not done from the beginning and people start to add their own
> controller drivers as if it was a flash device driver it becomes messy
> pretty quickly and people add hacks to support that (look at the raw
> NAND framework if you need a proof). So, I'd recommend having this
> separation now, even if the onle controllers we support have a 1:1
> relationship between HB controller and HB device.
> 
>>

Alright, will separate controller and slave representation. Thanks for
the feedback!


-- 
Regards
Vignesh