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

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Date:	Tue, 26 Nov 2013 13:26:44 -0500
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Sekhar Nori <nsekhar@...com>
CC:	"Khoronzhuk, Ivan" <ivan.khoronzhuk@...com>,
	Rob Landley <rob@...dley.net>,
	Russell King <linux@....linux.org.uk>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"Strashko, Grygorii" <grygorii.strashko@...com>,
	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>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 07/12] memory: davinci-aemif: introduce AEMIF driver

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:
>>>> Add new AEMIF driver for EMIF16 davinci controller. The EMIF16 module
>>>> is intended to provide a glue-less interface to a variety of
>>>> asynchronous memory devices like ASRA M, NOR and NAND memory. A total
>>>> of 256M bytes of any of these memories can be accessed at any given
>>>> time via four chip selects with 64M byte access per chip select.
>>>>
>>>> Synchronous memories such as DDR1 SD RAM, SDR SDRAM and Mobile SDR
>>>> are not supported.
>>>>
>>>> See http://www.ti.com/lit/ug/sprugz3a/sprugz3a.pdf
>>>>
>>>> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@...com>
>>>> ---
>>
>> [...]
>>
>>>> +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.

Regards,
Santosh
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