linux-kernel - Re: [PATCH 00/11] ARM: at91: remove !DT support for at91rm9200

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Message-ID: <20141128003938.7efb4ea0@bbrezillon>
Date:	Fri, 28 Nov 2014 00:39:38 +0100
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	linux-kernel@...r.kernel.org,
	Ludovic Desroches <ludovic.desroches@...el.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
Subject: Re: [PATCH 00/11] ARM: at91: remove !DT support for at91rm9200

Hi Arnd,

On Fri, 28 Nov 2014 00:12:25 +0100
Arnd Bergmann <arnd@...db.de> wrote:

> On Thursday 27 November 2014 18:12:43 Alexandre Belloni wrote:
> > 
> > As discussed some weeks ago, I prepared patches to switch sama5d[3-4] to
> > multiplatform. We are still missing the SMC and matrix drivers to switch
> > sam9 and rm9200.
> 
> I just looked at the drivers because I got curious, and to see if
> there are still any low-hanging fruit, but I guess you already picked
> them all ;-)
> 
> > The currently affected drivers are:
> >  - drivers/ata/pata_at91.c (SMC)
> >  - drivers/pcmcia/at91_cf.c (SMC)
> 
> I guess the SMC should live in drivers/memory with an interface
> similar to mvebu-devbus.c?

Actually, there's some work in progress to support the EBI/SMC blocks
as a memory controller driver ;-):

http://thread.gmane.org/gmane.linux.kernel/1822096

I'll post a new version soon.

> 
> Seems doable but nontrivial.
> 
> >  - drivers/usb/gadget/udc/at91_udc.c (Matrix, this is the only one
> >    for sam9)
> 
> Is at91_matrix a pin controller? With the board files removed, the udc
> driver has the only two remaining calls to at91_matrix_{read,write}
> for setting the pullup, so that could be modeled as a trivial pinctrl
> driver

The matrix block is containing several system configuration registers.
Most of them are related to AHB/APB bus config (master <-> slave
priority, burst and some other configs I don't remember).
Another register is here to define which HW logic is attached to an
external device connected through the EBI (External Bus Interface):
NAND, SDRAM, CompactFlash, ...
And, as you pointed out, there's a register to configure the pullup of
the UDC device.

As you can see, the matrix registers might be accessed by different
drivers (include the EBI/SMC driver), hence I proposed to expose them as
a syscon device (see the EBI/SMC series).

Best Regards,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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