linux-kernel - Re: [PATCH 05/36] mtd: nand: omap: Move IRQ handling from GPMC to NAND driver

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Date:	Fri, 13 Jun 2014 00:58:57 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Roger Quadros <rogerq@...com>
Cc:	dwmw2@...radead.org, computersforpeace@...il.com,
	kyungmin.park@...sung.com, pekon@...com,
	ezequiel.garcia@...e-electrons.com, javier@...hile0.org,
	nsekhar@...com, linux-omap@...r.kernel.org,
	linux-mtd@...ts.infradead.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/36] mtd: nand: omap: Move IRQ handling from GPMC to
 NAND driver

* Roger Quadros <rogerq@...com> [140613 00:40]:
> On 06/13/2014 10:18 AM, Tony Lindgren wrote:
> > * Roger Quadros <rogerq@...com> [140611 01:58]:
> >> Since the Interrupt Events are used only by the NAND driver,
> >> there is no point in managing the Interrupt registers
> >> in the GPMC driver and complicating it with irqchip modeling.
> >>
> >> Let's manage the interrupt registers directly in the NAND driver
> >> and get rid of irqchip model from GPMC driver.
> >>
> >> Get rid of IRQ commands and unused commands from gpmc_configure() in
> >> the GPMC driver.
> > 
> > This seems like a step backward to me. The GPMC interrupt enable
> > register can do edge detection on the wait pins, how is that
> > limited to NAND?
> 
> OK. But wait pin edge detection was not yet being used and I couldn't
> think of how it would ever be used. Any ideas?

Maybe to wake-up the system on bus activity or something? 

> > Further, let's not start mixing GPMC hardware module register
> > access with the NAND driver register access. They can be clocked
> > separately. And bugs in the NAND driver can cause issues in other
> > GPMC using drivers.
> 
> I understood that NAND controller is integrated into the GPMC module and they are clocked
> the same. Not sure why the hardware designers would keep the registers so closely knit.

Yeah. Maybe regmap could provide some abstraction to the the
NAND registers.
 
> FYI. memory/ti-amif.c and mtd/nand/davinci_nand.c share the AMIF register space in the
> same way. I thought it'd be nice to be consistent across TI drivers.

Probably they did not yet learn the problems caused by it :)

Regards,

Tony
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