linux-kernel - Re: [PATCH v3 06/10] mtd: brcmstb

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Date:	Thu, 07 May 2015 12:01:02 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Brian Norris <computersforpeace@...il.com>
Cc:	linux-mtd@...ts.infradead.org, Dmitry Torokhov <dtor@...gle.com>,
	Anatol Pomazao <anatol@...gle.com>,
	Ray Jui <rjui@...adcom.com>,
	Corneliu Doban <cdoban@...adcom.com>,
	Jonathan Richardson <jonathar@...adcom.com>,
	Scott Branden <sbranden@...adcom.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Rafał Miłecki <zajec5@...il.com>,
	bcm-kernel-feedback-list@...adcom.com,
	Dan Ehrenberg <dehrenberg@...omium.org>,
	Gregory Fong <gregory.0xf0@...il.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Kevin Cernekee <cernekee@...il.com>
Subject: Re: [PATCH v3 06/10] mtd: brcmstb_nand: add SoC-specific support

On Wednesday 06 May 2015 13:49:10 Brian Norris wrote:
> On Wed, May 06, 2015 at 09:12:43PM +0200, Arnd Bergmann wrote:
> > On Wednesday 06 May 2015 10:59:50 Brian Norris wrote:
> > > +       /*
> > > +        * Some SoCs integrate this controller (e.g., its interrupt bits) in
> > > +        * interesting ways
> > > +        */
> > > +       if (of_property_read_bool(dn, "brcm,nand-soc")) {
> > > +               struct device_node *soc_dn;
> > > +
> > > +               soc_dn = of_parse_phandle(dn, "brcm,nand-soc", 0);
> > > +               if (!soc_dn)
> > > +                       return -ENODEV;
> > > +
> > > +               ctrl->soc = devm_brcmnand_probe_soc(dev, soc_dn);
> > > +               if (!ctrl->soc) {
> > > +                       dev_err(dev, "could not probe SoC data\n");
> > > +                       of_node_put(soc_dn);
> > > +                       return -ENODEV;
> > > +               }
> > > +
> > > +               ret = devm_request_irq(dev, ctrl->irq, brcmnand_irq, 0,
> > > +                                      DRV_NAME, ctrl);
> > > +
> > > +               /* Enable interrupt */
> > > +               ctrl->soc->ctlrdy_set_enabled(ctrl->soc, true);
> > > +
> > > +               of_node_put(soc_dn);
> > > +       } else {
> > > +               /* Use standard interrupt infrastructure */
> > > +               ret = devm_request_irq(dev, ctrl->irq, brcmnand_ctlrdy_irq, 0,
> > > +                                      DRV_NAME, ctrl);
> > > +       }
> > > 
> > 
> > It looks to me like this should be handled as a nested irqchip, so the node
> > you look up gets used as the "interrupt-parent" instead, making the behavior
> > of this SoC transparent to the nand driver.
> 
> You snipped the rest of the patch, which involves more than just IRQ
> handling. The same registers touch both interrupts and data bus endian
> configuration, so it can't possibly be done transparently to the NAND
> driver.

Anything else in there? The bus configuration would just involve writing
a constant value in some register, right? Doing that in the irqchip
is also a bit ugly, but may still be better overall than doing it the
way you have above.

> > We recently merged nested irqdomain support as well, which might help here,
> > or might not be needed.
> 
> I'm not familiar with nested irqdomains. Do they address anything like
> the above problem?

The problem that nested irqdomains address is when an interrupt is handled
by two irqchips, in particular when one irqchip handles a virtual interrupt
number that was claimed by another irqchip already.

	Arnd
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