netdev - Re: [PATCH net-next-2.6 v3 1/1] can: c_can: Added support for Bosch C

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Message-ID: <20110111230539.GC18762@pengutronix.de>
Date:	Wed, 12 Jan 2011 00:05:39 +0100
From:	Wolfram Sang <w.sang@...gutronix.de>
To:	Marc Kleine-Budde <mkl@...gutronix.de>
Cc:	Wolfgang Grandegger <wg@...ndegger.com>,
	Bhupesh SHARMA <bhupesh.sharma@...com>,
	"Socketcan-core@...ts.berlios.de" <Socketcan-core@...ts.berlios.de>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Oliver Hartkopp <socketcan@...tkopp.net>
Subject: Re: [PATCH net-next-2.6 v3 1/1] can: c_can: Added support for
 Bosch C_CAN controller


> platform bus bindings. The question might be do we need the platform bus
> bindings or is it better to have AMBA bindings? The platform driver
> supports 16 and 32 bit attached devices, via IORESOURCE_MEM_{16,32}BIT.

platform_bus might be more generic. Depends on how many possibilities there
exist to connect the core to $something.

> Where do we have to look for the AMBA id registers?

I'll let the code speak (drivers/amba/bus.c):

	/*
	 * Read pid and cid based on size of resource
	 * they are located at end of region
	 */
	for (pid = 0, i = 0; i < 4; i++)
		pid |= (readl(tmp + size - 0x20 + 4 * i) & 255) <<
			(i * 8);
	for (cid = 0, i = 0; i < 4; i++)
		cid |= (readl(tmp + size - 0x10 + 4 * i) & 255) <<
			(i * 8);

	amba_put_disable_pclk(dev);

	if (cid == AMBA_CID)
		dev->periphid = pid;

	if (!dev->periphid)
		ret = -ENODEV;

with AMBA_CID being (include/linux/amba/bus.h):

	#define AMBA_CID        0xb105f00d

periphid is used to match the driver to the device then. If done correctly, it
should have been registered with ARM Ltd. before (AFAIK).

Good night,

   Wolfram

-- 
Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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