linux-kernel - Re: [PATCH 07/12] memory: davinci-aemif: introduce AEMIF driver

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Date:	Wed, 27 Nov 2013 12:22:11 +0200
From:	"ivan.khoronzhuk" <ivan.khoronzhuk@...com>
To:	Brian Norris <computersforpeace@...il.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>
CC:	Sekhar Nori <nsekhar@...com>, Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"Strashko, Grygorii" <grygorii.strashko@...com>,
	Russell King <linux@....linux.org.uk>,
	Pawel Moll <pawel.moll@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...nel.crashing.org>,
	Rob Herring <rob.herring@...xeda.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	Rob Landley <rob@...dley.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 07/12] memory: davinci-aemif: introduce AEMIF driver

On 11/27/2013 02:37 AM, Brian Norris wrote:
> On Tue, Nov 26, 2013 at 01:26:44PM -0500, Santosh Shilimkar wrote:
>> On Tuesday 26 November 2013 12:21 PM, Sekhar Nori wrote:
>>> On 11/26/2013 8:35 PM, Santosh Shilimkar wrote:
>>>> On Tuesday 26 November 2013 02:20 AM, Sekhar Nori wrote:
>>>>> On Monday 11 November 2013 10:36 PM, Khoronzhuk, Ivan wrote:
>>>>>> +static int davinci_aemif_probe(struct platform_device *pdev)
>>>>>> +{
>>>>>> +       int ret  = -ENODEV, i;
>>>>>> +       struct resource *res;
>>>>>> +       struct device *dev = &pdev->dev;
>>>>>> +       struct device_node *np = dev->of_node;
>>>>>> +
>>>>>> +       if (np == NULL)
>>>>>> +               return 0;
>>>>>> +
>>>>>> +       if (aemif) {
>>>>>> +               dev_err(dev, "davinci_aemif driver is in use currently\n");
>>>>>> +               return -EBUSY;
>>>>>> +       }
>>>>>
>>>>> Why expressly prevent multiple AEMIF devices? Its entirely conceivable
>>>>> to have two memories like NAND and NOR flash connect to two different
>>>>> AEMIF interfaces.
>>>>>
>>>> Ivan wanted me to clarify the Keystone hardware which supports
>>>> 1 instance of controller with 4 CS. That allows already four
>>>> devices to be connected. Currently NAND and NOR are connected on it
>>>> and two more slots are free.
>>>>
>>>> Since driver support what hardware is, lets not build a driver for
>>>> hardware which don't exist. And if at all such a support would be
>>>> needed in future, we can always add it.
>>>
>>> I understand the lack of hardware part, but its common to write the
>>> driver such that it can handle multiple instances. Is there any gain on
>>> current hardware because of this check? From what I am hearing, the code
>>> in question wont be exercised at all. So why go all the way and add it
>>> in first place?
>>>
>> Fair enough. The check can be dropped.
>
> Hmm, while the sentiment expressed by Sekhar is noble (to avoid
> unnecessarily constraining the driver), removing the check is not
> enough. You're still using a global static variable 'aemif', and it is
> important not to accidentally re-use this struct if a second device ever
> becomes available. So for the current implementation, the check is
> necessary IMO. If instead, you were to make 'aemif' a per-device struct
> (like with platform_set_drvdata()), then you would not have this issue.
>
> Brian
>

Yes, that is the plan to make it a per-device.

-- 
Regards,
Ivan Khoronzhuk
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