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

[ivan.khoronzhuk]

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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